Category: lab day

Tomorrow’s Post, but Today

11:30 – I was making up nitrogen-free fertilizer stock solutions for biology kits yesterday when it struck me again as so odd that I’m using reagent-grade chemicals to make up fertilizer solutions.

Each of the solutions contains macro- and/or micro-nutrients. We have to supply them as three separate solutions because if you try combining them in the concentrations needed for stock solutions, you get a nasty precipitate.

So I made up 15 liters of Fertilizer A, enough for 120 kits at 125 mL/kit. Fertilizer A is basically just a concentrated solution of monopotassium dihydrogen phosphate and dipotassium monohydrogen phosphate. (You use a specific mix of the two chemicals to maintain the proper pH.) Fertilizer A supplies potassium and phosphorus, both of which are macro-nutrients (The “PK” in “NPK”). That solution, as expected, turned out clear and water-white.

I went on to make up 2 liters of Fertilizer C, which provides calcium, cobalt, and boron ions. Again, that solution turned out clear and water-white.

Ah, but then I went on to make up 4 liters of Fertilizer B, again enough for about 120 kits at 30 mL per bottle, and provides magnesium, iron, copper, manganese, molybdenum, and zinc ions. What a mess. There’s not a precipitate per se, but the solution is a cloudy brown. Cloudy enough that I don’t want to run it through my dispenser pump, which is a precision instrument. So I guess I’ll hand-fill 120 30 mL bottles. Better that than buy a new dispenser pump.

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Tuesday, 30 September 2014

08:18 – Here’s one for the books. A week or so ago, I needed to order 25 g or so of reagent-grade 1-naphthol to make up some modified Griess reagent for forensic kits. Fisher Sci didn’t have it in stock, so I went off in search of some 1-naphthol on the Internet. I found a vendor on eBay that was offering 25 g of RG 1-naphthol for $37, shipping from Japan, so I placed an order. This morning I got the following email (spacing and line breaks sic).

Dear Buyer

Thanks for your order again.
Your item is already shipped with safe packing.

In these days, Korea/Japan country’s post office & major courier denied
air-shipping of some reagent products.
Especially, when MSDS section 14 ‘Transport Information’ has some
Regulation/Hazard Class info,* it can be returned to us. *
*And some countries customs denied customs clearance of these items also.*

We know this reagent is not so danger but they do not accept our shipping
*So we have to change the bottle label of the reagent products to
‘safe-looking’ random label for fast shipping.*
*The attached label is not real info so you should remove it & write real
info when you receive it.*

We take picture of your real reagent products before remove the label.
*Please see the attached images. *

We’re sorry for it. But this is only way to ship your reagent in right time.
Please understand our situation & effort for customer satisfaction.


So, basically they’re breaking the law by intentionally mislabeling a bottle of chemicals with a fake label that bears no relation to the contents. I’m of two minds about reporting this to eBay. On the one hand, this company has broken many laws and regulations by intentionally mislabeling a chemical bottle. On the other hand, I don’t doubt that what they’re shipping me really is RG 1-naphthol and I understand why they’re avoiding stupid shipping regulations. I don’t have time right now to get involved in a mess, so I’ll probably just let it slide and use the 1-naphthol.

Work on the book progresses. I’m still in the stage where I’m stubbing things out, recording thoughts as short sentence fragment placeholders as they occur to me, and so on, so it’s still a real mess. But I did manage to write more than 5,000 words yesterday on subjects ranging from guns to emergency heating alternatives to building a field-expedient sand/charcoal water filtration system with a 5-gallon bucket to building out a PERK (personal emergency relocation kit), and I have no doubt that I can continue doing 5,000 words a day for weeks on end.

Ebooks with large file sizes are problematic on Amazon because they charge a data transfer fee of $0.15/MB, which is deducted from the sale price before the royalty is calculated. On a standard all-text ebook priced at $2.99 to $9.99, Amazon pays a 70% royalty after minor deductions. A $3.00 ebook earns the author about $2.04 per copy in royalties after all is said and done, leaving Amazon’s cut at $0.96.

On ebooks priced at $2.98 or less or $10.00 or more, Amazon pays only a 35% royalty, but doesn’t charge the data-transfer surcharge, which is why most image-heavy ebooks sell in the $15+ range. For example, O’Reilly/MAKE prices our Illustrated Guide to Home Biology experiments at $15.39. They had to price it over $10, or they’d have to pay the $0.15/MB data transfer surcharge on a very large file. At $15.39, Amazon doesn’t collect the data transfer surcharge, but they pay only the 35% royalty rate, or $5.39 per copy. So, on each copy sold, Amazon keeps $10, and O’Reilly/MAKE splits $5.39 with us.

So, given the economics involved and also considering that PDFs suck on the Kindle, I’ve decided to publish the book in text-only form for the Kindle on Amazon, using AZW/MOBI/PRC format, probably priced at $3.99 or perhaps higher. But I’ll also provide buyers with a link to download a free copy of the full PDF version with high-res color images. Based on experience and the number of images I intend to include, I’d guess that full PDF version will probably run at least 200 MB and maybe more.

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Friday, 5 September 2014

07:55 – We’re all caught up on shipping kits. The only orders outstanding are the ones that came in overnight and this morning, which we’ll ship this afternoon. Meanwhile, I need to make up a bunch of solutions today and get started on bottling them.

One of those solutions is 4 liters of 6M sodium hydroxide, which has gotten me thinking about chemical storage. I’m down to my last three 500 g bottles of sodium hydroxide. When I finish those, I have to open a new container of sodium hydroxide, which in this case is a 10 kilo bucket rather than a 500 g bottle. Right now, that 10 kilo bucket is sitting on the floor because it won’t fit my storage shelves.

When we got started building science kits a few years ago, I put up shelves for chemical storage. Most of them are 4″ (10 cm) wide with vertical separation of 6″ (15 cm). Those worked fine when I was buying chemicals in 25 g, 100 g, and 500 g bottles. They’re not wide enough now that I’m buying a lot of chemicals in 1-kilo, 2- or 2.5-kilo, 5-kilo, and 10-kilo containers. That’s why there are still a couple of cartons of chemicals from Fisher Scientific sitting on the floor where UPS delivered them. I thought about repackaging them into 500 g and one kilo bottles, but that’s just too much work. Instead, I think I’ll remove some of the smaller shelves and replace them with wider shelves with more vertical separation. But that’ll have to wait for things to calm down a bit around here.

11:02 – I’d forgotten how obnoxious lead acetate is. We provide a 0.1 M solution of lead acetate in many of our kits, and I was just making up four liters of the stuff. I weighed out the appropriate mass of reagent-grade lead acetate and added it to distilled water. One might expect a nice, clear water-like solution to result. Instead, one gets a solution that looks like milk, literally.

The problem is that most common lead salts, with the exceptions of the acetate and the nitrate, are extremely insoluble in water. And water exposed to air just loves to suck up carbon dioxide. At room temperature, a liter of water dissolves about 1.6 grams of carbon dioxide. That doesn’t sound like much, but with the molar mass of carbon dioxide about 44 g/mol, that means that plain water exposed to air is actually about 0.036 molar with respect to carbon dioxide. That carbon dioxide reacts with water in a reversible reaction to form carbonic acid, the acid whose salts are carbonates. And lead carbonate is extremely insoluble in water, which is why my solution looks like milk. That 0.036 molar carbonic acid reacts 1:1 with my 0.1 molar lead acetate solution precipitating out nearly a third of the lead ions as insoluble carbonate. What’s worse is that that reaction removes the carbon dioxide from the solution, so it promptly sucks more carbon dioxide out of the air, until all the lead is precipitated and the solution reaches equilibrium with about 1.6 g/L of dissolved carbon dioxide. Basically, my dilute solution of lead acetate eventually turns into a dilute solution of acetic acid with most of the lead precipitated out as lead carbonate.

Fortunately, one can use Le Chatelier’s principle to shift the equilibrium by dissolving the lead acetate in a dilute solution of acetic acid rather than plain water. Although it’s a weak acid in absolute terms, acetic acid is a much stronger acid than carbonic acid. That forces the equilibrium of the reversible carbon dioxide <-> carbonic acid reaction to the left, keeping the dissolved carbon dioxide in the form of the molecular gas rather than the carbonate ion. And the lead acetate remains in solution as lead acetate.

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Thursday, 4 September 2014

08:08 – Being a chemistry geek, I get excited about things that other people don’t even notice. For example, yesterday I was making up solutions for kits. One of the solutions I made up was the IKI (iodine/potassium iodide) solution (Lugol’s solution) that’s included in most of our kits.

Iodine is extremely insoluble in water, something like 290 mg/L (290 ppm) at room temperature. Potassium iodide, on the other hand, is extremely soluble in water, something like 1,400 g/L at room temperature, or almost 5,000 times more soluble than iodine. The interesting thing is that iodine is very freely soluble in solutions of iodide ions, and the more concentrated the iodide solution, the faster the iodine goes into solution.

In the past, I’ve made up two liters of IKI solution by dissolving 40 grams of potassium iodine (KI) in about 400 mL of water, adding 25.4 grams of crystal iodine, swirling the bottle periodically over the day or so that it takes the iodine to go into solution, and then making up the solution to two liters. Yesterday, I decided to see if I could speed things up a bit by using much less water initially.

So weighed out 40 g of KI and transferred it to a 125 mL bottle. Ordinarily I’d have added some water at that point to dissolve the KI, but instead I weighed out 25.4 g of iodine crystals and added them to the bottle, right on top of the solid KI. Before I had time to add any water, a reaction started. A solid-state reaction, in which the solid molecular iodine started to react with the solid potassium iodide, producing essentially potassium tri-iodide in solid form. I could actually watch the reaction progress, starting with a bottom white layer of KI and a top dark-gray layer of iodine crystals. The two layers began to merge into a single dark brown layer.

I watched that happening for a few seconds and then added 60 mL of so of distilled water and capped the bottle. I inverted the bottle several times to mix the contents and all of the solids went into solution almost instantly. Because dissolution of KI is endothermic, the bottle quickly became quite cold. Even though the air in the house is air conditioned and dehumidified, water vapor immediately started condensing on the surface of the bottle and running down the sides. This whole process is fascinating in so many ways: kinetically, thermodynamically, and enthalpically. It’s good to be a geek.

11:55 – A few years ago, Barbara literally knocked over a hornets’ nest while she was working in the back yard. She was stung badly, and she’s understandably afraid of hornets and similar stinging insects. A week or so ago, she mentioned that there was a nest of yellow jackets or hornets down at the back of our property, apparently inside the trunk of a tree. So I walked down there after dark that evening and took along a can of hornet/wasp killer. One of those that shoots a stream instead of a fine mist. I walked over to where I’d seen the bugs clustering earlier that day, and hosed it down with the hornet/wasp killer. They immediately swarmed out of the nest, but I turned off my flashlight and walked away unstung. The next day, I noticed there were a lot of dead bodies lying near the nest entrance, but there were still a lot of them swarming around. So I went down again that night and sprayed again. The next day, same deal. I got some of them but there are a lot left. I understand that nest may be buried deeply and contain literally thousands of the things.

If I were living in an Agatha Christie novel, I’d use something that actually kills them, like potassium cyanide. A couple tablespoons of that in the nest entrance and a bit of sulfuric acid would fumigate the hell out of that next. I have both of those in my lab, but I think I’ll take a more traditional approach.

I search the web for stinging insects in North Carolina, attempting to identify the species, but I haven’t gotten a close enough look at one to be sure. There are several candidates, and the advice for all of them on the NC Ag Extension web site is similar. First, just leave them alone unless they present a real threat to people. Second, if you have to kill them use something like the Spectrocide/Hot Shot insect spray I used, following the label directions strictly, of course. But the site warns that it probably won’t be effective and even several treatments may leave a viable nest. It does say that the colony dies out in the winter and is seldom re-used the next year.

The site also says whatever you do, don’t use gasoline because it’s harmful to the environment. I take that to mean that gasoline will in fact kill all of the little SOBs but using it would violate federal law. Federal law, of course, ignores the fact that these stinging insects are very harmful to our environment. I’m thinking napalm.

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Sunday, 31 August 2014

10:41 – Barbara is ironing and cleaning house while I do kit stuff. Right now, I’m dehydrating some magnesium sulfate heptahydrate to anhydrous form. The hydrated form, AKA Epsom salts, is cheap, a couple bucks a kilo in USP/FCC form, which is as pure as reagent grade. Buying the anhydrate from a chemical supplier runs $80 to $100 per kilo, which is outrageous.

So I just spread about a kilo of Epsom salts in a large casserole dish and stuck it in the oven at 500F (260C) for an hour. That removes most of the water of hydration and forms a thin glassy layer of magnesium sulfate. I break that into chunks and toss it into a blender that I reserve for such work. I then blend it on high to break up the chunks into mostly powder, run it through a flour sifter, repeat as necessary until all the chunks are broken up, and then put the powder back in the oven for another hour at 500F to finish drying it out. I do this while I’m doing other stuff, so the whole process requires maybe ten minutes of my time. Add the cost of my time to maybe two or three bucks in materials cost and electricity, and I end up with half a kilo of magnesium sulfate anhydrate for less than $20, even billing myself at $100/hour.

The price of many chemicals has gotten ridiculously high. For example, we use copper(II) acetate to make up Barfoed’s reagent, which is essentially a 0.5 molar solution of copper(II) acetate with 10 mL of glacial acetic acid added per liter. I was about to order some copper(II) acetate, but found my regular supplier wanted $120/kilo. Geez.

So, the next time I need to make up Barfoed’s reagent I’ll do it from scratch on the fly. I generally make up four liters at a time, so I’ll start with two clean 2-liter Coke bottles. I’ll transfer two moles of copper(II) sulfate to one bottle. That copper(II) sulfate is from Home Depot, which sells a 2-pound (907 g) bottle of the stuff for about $10 under the name of Root Kill. The assay on the bottle says it’s 99% copper(II) sulfate, which I’ve verified gravimetrically. The remaining <1% by mass is mostly insoluble copper oxide. The molar mass of copper(II) sulfate is 249.68 g/mole. Dividing that by 0.99 gives 250.22 g/mole, so I'll transfer 500.44 g of the Root Kill to the two liter bottle and dissolve it in hot water. (It dissolves quickly in hot water; in room temperature water it can take literally a week to dissolve.) I'll then filter the resulting two liters of pretty blue solution into the second bottle, rinse out the first bottle, and divide the solution with one liter in each of the two bottles. So far, I'll have used up maybe five minutes of actual working time and about $5 worth of the Root Kill.

I’ll then add either sodium carbonate or sodium bicarbonate, both of which are cheap, to precipitate the copper ions as insoluble copper(II) carbonate. Once the precipitate settles, I’ll decant off the supernatant liquid, which contains mainly sodium sulfate with a small amount of the excess sodium carbonate or bicarbonate in solution. If I decant 90% of the supernatant liquid and refill the bottle with tap water, I’ve diluted the original level of soluble contaminants to 10% of what they were. Repeating that process a few times, ending with a distilled water wash, reduces the soluble contaminants to 1%, 0.1%, 0.01%, and finally 0.001%, which is better than good enough.

I don’t even need to filter out the copper(II) carbonate and dry it. I can simply wet it with a liter or so of distilled water and add glacial acetic acid stoichimetrically to convert the copper(II) carbonate to copper(II) acetate in situ, add an extra 20 mL of the glacial acetic acid, and then bottle the resulting Barfoed’s reagent.

And don’t get me started on ammonium metavanadate. The last time I bought it, maybe three or four years ago, I paid something like $15 for a 25 gram bottle. I thought $0.60/gram was pretty high then, but that’s now tripled to nearly $2/gram, and that doesn’t even include the required poison-pack container and hazardous shipping surcharge. Geez. I can synthesize the stuff from scratch here for something like $0.05/gram, and it’s no more difficult than the copper(II) acetate synthesis.

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Thursday, 28 August 2014

07:57 – So, I was down in the lab yesterday making up a new batch of Kastle-Meyer reagent, which is used in forensic science as a presumptive test for blood. It’s made by dissolving phenolphthalein powder in a concentrated solution of potassium hydroxide and then refluxing it over powdered zinc until the intense pink color of phenolphthalein in basic solution fades to colorless as the phenolphthalein is reduced to phenolphthalin.

Even cold, concentrated solutions of strong bases like potassium hydroxide etch/dissolve glass, and if they’re boiling they do so very quickly. Within a couple of minutes, the glass starts to turn cloudy with chalky white streaks. Once a flask is used to make up KM reagent, it’s too ugly to even consider using for anything else. So, the first time I made up a big batch of KM reagent a couple of years ago, I devoted a 2 L Erlenmeyer flask to the job, and that’s all I’ve used it for ever since. For the first batch, I put a kilo or so of zinc powder in the flask, made up the KM reagent, and then washed the flask out with several changes of water, leaving the unreacted zinc powder in the bottom of the flask. I store the flask full of water and stoppered, because damp zinc powder is pyrophoric (catches fire spontaneously when exposed to air). The next time I need to make up a batch, I drain the water, rinse the zinc several times, and use it again for that batch. I’ve done that several times over the last couple of years, and it’s always worked as expected.

Normally, I just add a liter of water to the flask along with the appropriate amounts of potassium hydroxide and phenolphthalein powder, put it on the hot plate, bring it to a boil, and then let it reflux for a few minutes. As it simmers, the bright pink color starts to fade and after five or ten minutes the solution turns colorless. But yesterday it didn’t work. After sitting there refluxing for half an hour or more, the solution was as pink as ever. Hmmm. Obviously, the zinc wasn’t reducing the phenolphthalein to phenolphthalin. It looked like there was still plenty of zinc in the flask, but instead of powder it looked more like a zinc coral reef. So I transferred another couple hundred grams of zinc powder to the flask. Sure enough, within five minutes the solution had turned colorless. The moral here is that just because it looks like there’s plenty of zinc remaining doesn’t mean there is.

10:45 – I get a surprising amount of private email from preppers, many of which ask me science-related questions. Sometimes they link to threads on various prepper forums. For example, one topic that I’m frequently asked about is storing antibiotics. The usual questions have to do with how long various antibiotics can be stored and the suitability of veterinary antibiotics for human use. I’m always surprised by how bad the information is on many of these threads, including quite a few comments by physicians, who should know better.

With regard to shelf life, the real answer is that most antibiotics if stored in the freezer will still be usable 20 or more years from now. Their potency may decline a bit, but long-term tests have shown that most antibiotics lose 10% or less (often, much less) of their potency after being stored frozen for 10 years. Just as important, any degradation that does occur does not create toxic byproducts. The one exception is the tetracyclines, which should not be stored long term. Tetracyclines do in fact produce hepatotoxic and nephrotoxic degradation products. Administering old tetracycline or its derivatives can kill the patient from liver or kidney failure.

With regard to human use of veterinary antibiotics, that’s generally not a problem. It’s not like pharmaceutical companies produce amoxicillin for humans in one plant and amoxicillin for veterinary use in another. It all comes from the same vats, and veterinary medications are packaged as carefully as human medications. One problem arises because people are not dogs or cows or chickens. The mechanisms are very similar in any of these animals, including humans, but our internal organs and processes may differ, sometimes significantly.

For example, on one forum thread someone asked if erythromycin packaged for oral veterinary use was suitable for oral human use. A physician responded that it was fine. It’s not. Veterinary erythromycin for oral use is often in the form of the phosphate salt. That’s fine if you’re treating chickens or turkeys. In humans (or other mammals), not so good. The problem is that the phosphate salt is quickly broken down by human gastric juices and the erythromycin is destroyed before it can be absorbed. Erythromycin for oral use in mammals is compounded with a different anion that renders the salt much less subject to being broken down by the hydrochloric acid in mammalian stomachs.

I keep a pretty good stock of veterinary antibiotics. For example, I order penicillin G potassium and sulfadimethoxine literally by the kilo for use in biology kits. Neither is intended for human use, but both are usable. The penicillin G potassium is not ideal for oral human use because it’s also degraded by stomach acids, but it can be used orally by increasing the dose and administering it when stomach acid is minimal, such as an hour or so before meals. One can also administer sodium bicarbonate (baking soda) a few minutes before the antibiotic to reduce stomach acidity even further. The sulfadimethoxine has never been approved for human use in the US, but it’s widely used in other countries, particularly Russia, and has been for decades. It’s as effective as the other sulfas on organisms susceptible to sulfas, and it has the added advantage of a very long biological half-time. That means it needs to be administered only once per day rather than the every four hours typical for short-acting sulfas.

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Wednesday, 18 June 2014

08:14 – Two days down, three to go until Barbara returns home. Colin slept through the night last night. The night before, I think he was expecting Barbara to come home, so he got excited every time he heard a sound that might be her returning. The official high in Winston-Salem yesterday was 92F, but according to both our outdoor thermometers it got to just over 95F here.

Today I’ll continue making up chemicals and filling bottles.

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Tuesday, 17 June 2014

08:18 – One day down, four to go until Barbara returns home. Colin behaved pretty well yesterday, but last night was horrible. On average, every 45 minutes or so he’d jump down off the bed and go roaring down the hall to the front door, barking his head off. I’d just about get back to sleep when he’d do it again.

It’s not yet summer, but things are warming up around here. Our highs for the next week are to be around 95F (35C), with lows in the low 70’s (~ 22C). Thunderstorms are in prospect just about every day.

This morning I need to make up three liters each of Barfoed’s, Benedict’s, and biuret reagents, and 12.5 liters of Fertilizer concentrate A. Once I get those bottles filled, we’ll have all the chemicals we need to make up another 30 biology kits, and most of what we need for 60 or 70 more beyond that. And then I can get to work on making up chemicals for another batch of forensic kits.

15:57 – I just got email from Netflix saying that they’ve (finally) added season five of Heartland. Now they’re only two seasons behind. Speaking of Heartland, I’m now just over halfway through season two. With three evenings left until Barbara returns, I should get through season two and well into season three. I was considering the wild-women-and-parties thing last night, but Colin preferred to watch Heartland re-runs. He really likes hearing Amy say, “Good boy!” He thinks she’s calling him a good boy.

I now have all the chemicals made up for more biology kits. Tomorrow I’ll start on the ones I need for forensic science kits, which we’re getting low on. That includes one of my least favorite chemicals, black fingerprint powder. Our fingerprint powders use a proprietary formulation, but the white powder is a mixture of titanium dioxide, calcium carbonate, and cornstarch, while the black powder is a mixture of lampblack and graphite. The problem with the black powder is that it gets on everything and produces black smudges that are difficult to remove. I’ll fill unlabeled containers with the black powder, seal them, and then wash them to remove any remaining powder before we label them. Even doing that, we may end up with some black smudges on labels.

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Thursday, 5 June 2014

08:07 – Public schools have been in the news here lately. With the Republicans firmly in control of state government, big changes to public education are in prospect.

Legislators are doing their best to do away with tenure for public school teachers. That suffered a setback recently when a liberal judge ruled that the state couldn’t take back something that had already been granted. I expect the state supreme court will reverse that decision. And North Carolina is withdrawing from Common Core, which the state just began implementing recently. A review panel has been set up, tasked with adopting new state curriculum standards, with the provision that Common Core is not acceptable even if the panel determines that it is the best available alternative. And legislators have carefully crafted a new law to get around US Supreme Court decisions on restricting religion in public schools.

The real problem is that the politicians have set their sights far too low. The fundamental problem is public schools, period. The North Carolina constitution requires the state to provide an elementary through high school education to all children. But the constitution doesn’t specify how that is to be done.

The solution is to establish an educational voucher system. A real one, one that is available to all students’ families rather than just a tiny percentage. And one that is funded directly by the pool of money allocated to public education. Those vouchers should be for the amount the state currently spends per student, and the amount of any voucher redeemed at a private school should immediately be deducted from the budget allocated to the public schools in that student’s district.

It’s also important that the state implement absolutely no requirements or standards for private schools, including any restrictions or requirements concerningn secular versus religious, teacher certifications, and so on. It should be entirely up to the private schools themselves to set their own policies and to the parents and students to decide what constitutes an appropriate education.

The immediate result of such a true school choice program would be that public schools would have to compete efficiently and effectively in an educational free market if they want to survive at all. Most would not, and that’s all to the good. Would some students receive very poor educations? Of course they would, but almost certainly fewer than currently receive very poor educations in our existing public schools.

15:05 – I’ve been making up solutions and filling bottles all day, hundreds of bottles. And I just got to the next item on my to-do list, which is methyl red solution. Methyl red, AKA 2-(N,N-Dimethyl-4-aminophenyl)azobenzenecarboxylic acid, is extraordinarily insoluble in water. So much so that the solution we use, 0.02% w/v, exceeds the solubility of methyl red. That’s 0.2 g/L. If I simply add 0.2 g of methyl red to a liter of water, about 90% of it (at a guess) remains undissolved.

Fortunately, there’s a way around this. The sodium salt of methyl red is considerably more soluble than the free acid. Unfortunately, I wasn’t thinking about that when I ordered what amounts to a lifetime supply of the free acid. So I need to convert the free acid to the sodium salt. That’s easy enough to do: simply dissolve the methyl red free acid in a (very) dilute solution of sodium hydroxide to form a solution of sodium methylredate. (I lay claim to creating that anion name; Google finds zero instances of it.)

Just how dilute? Well, the stoichiometry says that one mole of sodium hydroxide reacts with one mole of methyl red. The molecular mass of the free acid is 269.30 g/mol, while that of sodium hydroxide is 39.9971 g/mol. But making up a liter of 0.02% methyl red requires only 0.2 g, or 0.00074+ mole. Accordingly, for a 1:1 correspondence, I need about 29.7 milligrams of sodium hydroxide. The standard 6 M sodium hydroxide solution that we supply with many of our kits contains 240 mg/mL, so I’d need to add about an eighth of a milliliter of that solution per liter. The plastic pipettes we buy 10,000 at a time deliver about 33 drops/mL, so call it four drops.

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Friday, 21 March 2014

09:45 – Lots of interesting comments and emails about yesterday’s post. Just to be clear, what I’m designing/building right now are the 144-hour (2-person-3-day/3P2D/4P/1.5D) duffel bags for Barbara’s and my vehicles. These aren’t zombie apocalypse kits, just short-term emergency kits in case we’re stranded in an ice storm or something. Everything should fit in a large duffel bag or two smaller duffels. Everything with a limited shelf life (batteries, drugs, light sticks, some foods, etc.) goes on top and gets checked/replaced annually. Otherwise, they just sit in the vehicles until needed. I’ll post a detailed checklist (including brand names) once I finalize it.

I’ll spend some time today making up more solutions for the kits. If I have time remaining, I’ll work on the earth/space science kit manual.

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