Historic Organic Extractions I: "On Milk, and its acid" by Carl Wilhelm Scheele

In the companion post previous to this one, I'm writing about historic methods of extracting organic chemicals. I was going to start with Scheele's methods of extracting lactic acid, but I can't find the details in any English sources. Images of the academic journal in which he posted about it are available on google scholar, but they're in Swedish, and I don't read Swedish. In this post I'll be transcribing the text and posting translations courtesy of Google Translate. So far the text is just talking about why cheese coagulates from milk when you apply acid and heat, but I expect things to improve as I continue. In my transcription, I'm currently missing some diacritical marks that might be important to the meanings of Swedish words, and also I'm occasionally mixing up a long-medial-s, "ſ" for an "f". Oops. I'll keep working to improve it.

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"Om Mjölk, och dess syra" af Carl Wilhelm Scheele

§. 1.

Det är bekant, at Ko-mjölk innehåller Smör, Ost, Mjölk-säcker, nagot extractist, litet falt, och at det ofriga ar vatten: men annu aterstar mycket, for at kunna fa en ratt chemisk kannedom i detta amne. Jag vill forst uppehalla mig litet vid Ostens atskiljande ifran vastlan, m. m. och fedan undersoka syran och defs egenskaper, fom vasslan eller jolken i varmen antager.

§. 2. a) Om nagon antigen vegetabilisk eller  mineralisk syra blandas i Mjolk, upkommer, son allmant bekant ar, en ystning. Denna ystning sker da allenast fullkomligen, nar blandningen underhjelpes med nagon varme, ty da fammanhanga Ost-particlarne, och utgora en massa. Om ystning sker med m ineraliska syror, sas Osten i mindre mangd, anom den sker med vegeetabiliska syror. b) Om uti kokande mjolk, lagges fa mycket af nagot neutral-falt, fom deruti kan uplofas, fkiljer Osten fig likaledes fran vasslan. Det famma hander ock med alla metalliska och medel-salter, samt med sacker och gummi arabicum.

§. 3. Caustika alkalier uplosa Osten medelst kokning, som med syror ater kan precipiteras; faledes kan man latt falla pa den tankan at Osten medelst nagot Alkali uti Mjolken vore uplost.

At utrona fanningen haraf, ystads Mjolken med litet, Salpeter-syra, vasslan filades och evaporerades, men gaf omfider ej ringafte fparr pa Saltpeter utan allenast det vanliga Mjolk-fackret. Således maste Mjolkens ystning med syror hafva annan orsak.

§. 4. a) Den Ost, fom sas med mineraliska syror, vifar altid fparr pa syra, hvaraf ock en del uti kokande vatten kan uplofas. b) Om til en del nyfs praecipiterad otorkad Ost, tagas 8 delar vatten, hvartil blandas fa mycket af nagon mineralisk syra, vid vattnet far fyrlig fmak, samt, tedan kokas; uploset Osten. Vegetabilisk syror och mjolk-syra losa litet eller ingen Ost. Haraf fer man orsaken, hvarfore ftorre myckenhet Oft erhalles, nar Mjolken yftas med vegetabiliska, an emd mineraliska syror (§. 2. a.) Har finner man ock igen grunden til Mjolkens ystning med syror. Osten attraherar nemligen en vifs mangd syra, och denna sorening fordrar langt ftorre mangd vatten, for at halla sig uplost, an mjolken med sig sorer. c) Blandas Mjlk med 10 delar vatten, fa fas med mineraliska syror ingen Ost. d) Om til deffa fyrliga Ost-uplosningar, tilflas af nagon concret mineralisk syra, fa praecipiteras ftorsta delen af Osten ater. Den falles likaledes af alkalier och kalk-vatten: men kommer for mycket til, uplofes Osten ater. e) Nar Osten, uti kalk eller caustikt alkali uplost, ater praecipiteras med attika, upkommer en oangenam hepatisk luckt.

Orsaken, hvarfore Neutral-och Medel-salter, Gummi och Sacker, Yfta Mjolken, (§. 2. lit. b) larer formodligen vara at finna uti vattnets narmare affinitet til dessa salter, an til Osten. Som adstringerande vaxters intusion alrid figver tecken til nagon fri och obunden syra, fa ar latt at forsta, hvarfore de ysta Mjolken; och som manga, om icke alla vaxter, med sig fora en oft-lik materia, fer man ock haraf orsaken, hvarfore China-decocter coagulera emulsioner.

§. 5. Hvad Ostens bestands-delar betrassar, ar det formodligen, fafom alla animaliska ger latinosa amnen, annu i fullt morker. Sa mycker ar fakert, at jorden i Osten ar den allmanna Terra animalis, och bestar af phosphorus-syra, mattad med ofverflodig kalk: emedan jag, medelst flere abstractioner med Saltpeter-syra otver Osten, omsider bekommit et hvitt residuum, som ar calx nitrata och terra animalis. Samma jord-art fick jag af residuum, efter Ostens destillation, och defs ytterligare calcination med saltpetrens tilhjelp uti digel, fom eljest utan saltpeter ar ganska fvar at forvandla i aska. 30 delar torkad Ost, innehaller omtrent 3 delar animalisk jord.

§. 6.

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I intend to provide the full text and the full translation, but a delightful Swedish acquaintance has been kind enough to translate section 8, which contains the lactic acid extraction. I'll reproduce his translation and notes here in full:

§8 I let the sour milk-whey evaporate, until about 1/8 remained, and all cheese had separated therefrom, whereupon I filtered the acid. To now get the terra animalis from her, I saw no other way, as lime water precipitates this soil type, than to saturate the acid with lime. When this was done, I filtered the solution, and diluted the same with 3 times as much water. To now get the lime from my menstruum, the sugar acid was an excellent means: I dissolved some of it in water and added then so much of the lime solution that no more calx saccharata precipitated, whereby I took great care not to add more of the sugar acid, than with lime water easily can be ascertained. Now remained the other substances which also should be separated from the milk acid. I therefore evaporated the acid, until it was as thick as honey, whereupon I dissolved this thickened acid in spiritus vini rectificassimus, whereby as well the milk sugar, as the other foreign, to the acid not belonging interfering substances where separated, and the acid alone in spiritus vini was dissolved, which I thereby filtered. To this acidic solution I added some clean water and distilled off spiritus again, whereupon the lactic acid remained so pure, as it, by my thoughts, with the aid of chemistry can become.

Note that 'soil type' is probably not a correct translation. Jordart is the swedish word he uses. Which can mean soil type but is more like an earth mineral quality. I hope you find a better word for it.

Note that he does not use the term 'lactic acid', but 'milk acid', and while it is called that in swedish, 'mjölksyra', I found it better to keep it as such, in order to go with his writing style. 

It's interesting to see a little of what science was like in the 17th century. Also Scheele is an important figure in the history of Sweden. He was born in occupied parts of what today is Germany and he lived in Köping, which is only an hour away from where I come from. He died 43 years old. In his life he discovered oxygen. Among, apparently, lots of other interesting things. I really enjoy the humble tone of his writing. A little before this paragraph 8, he talks about how eggwhite and cheese is basically the same substance, since it reacts in the same way to his experiments. And this sentence from paragraph 7 is just wonderful "As known, milk will in summer, in a short time, begin to sour and thicken."

Thanks, Mats!

A few notes of my own: sugar acid is an old name for oxalic acid. It was originally made by treating sugar with nitric acid. What kind of sugar? I saw a reference to sugar cane in one paper, but I'm not sure how far it was processed toward sucrose. Sucrose will work fine, and so will glucose and fructose if you have those. There are some byproducts like tartaric acid or erythronic acid, but it's a pretty simple recipe if you have access to nitric acid: 

1. Dissolve the sugar in water, add the concentrated nitric acid (like ~70%), stir with heat in a very well ventilated area to remove NO2 fumes, and remove from heat when the reaction starts going crazy, still stirring. The reaction will be hot, boiling, poisonously gaseous, blood red, and self-sustaining. It's pretty intense.  

2. When things have calmed down, boil the reaction products down to a reduced volume and allow the oxalic acid to crystallize out. This will happen fine at room temperature, and the crystals will go from reddish to white as the NO2 leaves. Wash the crystals cold water a few times if you want a smaller quantity of a purer product. 

It seems Torbern Olof Bergman was the first to publicize about this reaction, but Scheele had done it first. Both of them might have done it in 1776? 1776 might be the year that calcium oxalate was synthesized, although it had been isolated from natural sources earlier. Johan Afzelius might also deserve some credit as an early contributor. "Calx saccharata" is the calcium salt of this acid, a.k.a. calcium oxalate.

"Spiritus vini rectificassimus" is just concentrated ethanol.

Lime water is a solution of calcium hydroxide.

Terra animalis is bone ash. Bone ash is primarily composed of calcium and phosphate. The calcium phosphate mineral in non-calcined bones is hydroxypatatite, Ca5(OH)(PO4)3, and that's likely in bone ash, but I wouldn't be shocked if bone ash also had some regular calcium phosphate, Ca3(PO4)2 or even separate bits of calcium oxide or and phosphorous pentoxide, depending on the conditions of the heating (heat, duration, oxygen).

Let's recap the recipe:

1. Coagulate cheese curds from sour milk. Allow the whey to evaporate a lot and remove the separated cheese curds by filtration. I don't know what they used for filters back then. Coffee filter paper or cotton balls work fine today.

2. Apply a calcium hydroxide solution. This supposedly precipitates calcium phosphate salts. I didn't know that milk was rich in phosphoric acid, but maybe so if terra animalis is formed? Filter that out and retain the liquid. Dilute this with some water.

3. The lime water that we added got rid of the phosphorous, but now we want to remove the lime again. Next we add in oxalic acid, which produces a precipitate of calcium oxalate and leaves behind a solution with lactic acid. Scheele is careful to only apply oxalic acid as much as it keeps forming a precipitate and no more. Again, filter out the precipitate and retain the solution.

4. Boil the solution down to a thick consistency and add in concentrated ethanol, which will dissolve lactic acid but not some other impurities. The impurities can be filtered out. Finally he adds a little water and distills off the ethanol. My guess is that the lactic acid crystals remain in the pot rather than coming over in the distillate. And you'll probably have to cut the extraction short before dryness to avoid thermal decomposition and finish with some room temperature evaporation.

Pretty cool, right? Even briefer: Add calcium hydroxide water to concentrated sour whey to precipitate some garbage, and filter it out. Add oxalic acid to remove the calcium and filter that out too. Boil it down, dissolve in ethanol, filter one more time, and distill off the ethanol.

I'm quite impressed, honestly. He used the oxalic acid that he himself figured out how to produce, along with normal old calcium hydroxide and ethanol, to isolate something new from old sour cheese water. I have ready access to sugar and lime and ethanol and sour milk and never got close to doing that. I doubt I would have gotten closer if I had ready access to nitric or oxalic acid. And honestly, I've never lived anywhere that we didn't grow rhubarb, so I might have had ready access to oxalic acid too. Scheele was just a brilliant and dedicated man in his inventions and investigations.

Historic Organic Extractions

This post will be about historic methods used for the extraction of organic chemicals, especially organic acids and plant-derived alkaloids, with a special focus on the extractions done by Carl Wilhelm Scheele (1742 - 1786) and Henri Braconnot (1780 - 1855).

Regardless of who first extracted them, I also hope to touch upon these organic acids: (abietic, acetic, ascorbic, aspartic, benzoic, butyric, caffeic, citramalic, citric, ellagic, folic, formic, fumaric, galacturonic, gallic, glucuronic, glutamic, glutaric, glycolic, isocitric, lactic, maleic, malic, mycophenolic, nicotinic, oxalacetic, oxalic, p-coumaric, pantothenic, pectic, propionic, pyrogallic, pyruvic, quinic, salicylic, shikimic, sorbic, succinic, tartaric, uric)...

And these alkaloids: (aconitine, anisodamine, anisodine, berberine, boldine, coniine, ephedrine, caffeine, cephaeline, chaconine, chelidonine, cinchonidine, cinchonine, cocaine, colchicine, cytisine, ecgonine, emetine, ergine, ergotamine, erythravine, galantamine, harmaline, harmine, huperzine A, hyoscyamine/atropine, ibogaine, ibogaline, ibogamine, lobeline, lupinine, mescaline, morphine, nicotine, pentoxifylline, physostigmine, pilocarpine, piperine, protopine, psilocin, psilocybin, quinidine, quinine, reserpine, scopolamine/hyoscine, solanine, strychnine, theobromine, theophylline, tomatine, vinblastine, vincamine, vincristine, yohimbine).

This all started when I was reading about Henri Braconnot. He discovered pectin, glycine, chitin, ellagic acid, legumin, and nitrocellulose, among other things. The more I read about his discoveries, the more I felt that modern scientists have lost the knowledge of how we used to get our organic chemicals, where once this knowledge was common across the scientists of Europe.

Scheele was an ever greater giant of chemistry than Braconnot. In addition to many elements and mineral acids, he discovered (lactic, gallic, pyrogallic, oxalic, tartaric, malic, and uric) organic acids. He also isolated glycerin and lactose.

I have a feeling that the historic methods of Scheele and Braconnot will be readily adapted to the laboratory of the modern amateur home chemist, and that's one reason I'm investigating these things. Another reason is that we seem to have... misplaced our recipes? YouTube is full of historic cooking shows based on cookbooks going back to Roman times and before. It seems to me that the original recipe for isolating malic acid should have similar cultural standing as a colonial recipe for apple pancakes, at least among chemists. These recipes are our heritage and I'm eager to inherit them.

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Another cool earl chemist was Louis Nicolas Vauquelin, who supposedly discovered malic acid, camphoric acid, and quinic acid, along with some notable inorganic discoveries. Also with his assistant he co-discovered the first known amino acid, asparagine. He's often credited with discovering pectin, but he didn't isolate it, and people already knew about jam making, so I'm not sure what possible accomplishment of discovery remains for him to have made originally. 

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Looking these things up is surprisingly time consuming, and it seems like I might end up making separate posts for most of the chemicals. Maybe this post will organize them!

* I. Oxalic and Lactic acids

* II. Atropine (in progress)

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Citric acid: In 1784, Scheele published a method to isolated citric acid from lemon juice in an article titled "Anmärkningar om citronsaft och ett sätt att kristallisera den" (Remarks on lemon juice and a method of crystallizing it). In "The Chemical Works of Carl Wilhelm Scheele", Anders Lennartson shares the method, which I'll summarize here: 

Boil lemon juice. Add calcium carbonate, which will cause effervescence, and keeping adding it until the effervescence ceases. Allow the mixture to cool and calcium citrate will precipitate. Pour off the liquid and wash the solid until the washing water runs clear. Add very dilute sulfuric acid to the powder and boil for 15 minutes, producing a precipitate of calcium sulfate, which can be discarded by filtering. Add dilute sulfuric acid drop-wise to precipitate any remaining calcium. Crystallize the citric acid by concentrating the liquid through evaporation over gentle heat or by reducing the solubility of the solvent through cooling or through a combination of concentrating and cooling.

Scheele tried a different method before that which failed, and it's kind of interesting to compare the methods to see what differs: "Scheele evaporated lemon juice to the consistency of honey and extracted it with ethanol, which left a sticky substance. Scheele distilled off the ethanol and expected to get a pure acid, but still failed to crystallise it.  ... Scheele found that after precipitating the acid with lime, there was a residue which had a bitter taste and was soluble in both water and ethanol."

I think one lesson here is that plants have lots of chemicals and the success of extracting one chemical from the multitude can be very sensitive to small changes in your procedure. I don't know what the bitter residue was in the failed ethanol extraction (maybe some mix of flavonoids, carotenoids, limonoids, tannins, and terpenoids?), but probably the sulfuric acid is removing the bitter thing in the successful extraction method. My guess is that there's some way to use sulfuric acid in combination with the ethanol extraction method to get citric acid crystals, but it's great that Scheele found an isolation procedure that works and doesn't require a distillation.

: Pectin

Henri Braconnot discovered pectin and lectured on its isolation to the Royal Academic Society of Nancy in 1824 and published about it in Annales De Chimie Et De Physique volume 28 in 1825 in "Recherches sur un nouvel Acide universellement répandu dans tous les végétaux" ("Research on a new acid universally diffused in all plants"). I'm still translating, but here's a paragraph about a jelly-like acid he found in dozens of plants, and probably every plant he investigated: 

[I]t is very easy to obtain it from the various parts of plants. If we operate on roots which contain starch, such as those of celery or carrot, we reduce them to a pulp with the aid of a grater to squeeze out the juice; the marc is exhausted by boiling in water sharpened with muriatic acid, then washed and heated with an extremely diluted solution of potash or soda: a thick, mucilaginous, slightly alkaline liquor results, from which the muriatic acid separates the new acid in the form of an abundant jelly, which only asks to be well washed off: in this state it is scarcely colored, especially when it comes from the parts of the vegetables who are not. This jelly has a noticeably sour flavor. Applied to a paper dyed blue by litmus, it reddens it very distinctly, although it does not retain any foreign acid.

Maybe that's pectic acid and the actual pectin is later in the paper. I'll let you know. But it's probably pectin. That's my take. To summarize his procedure here: boil grated plant matter with hydrochloric acid, then heath with dilute potassium carbonate. A jelly separates out which can be washed clean of the source liquid.

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I was curious how pectin is extracted in the modern setting. I found some weird procedures with freeze driers and chromatography and stuff, but these excerpts of pages provided by google seem pretty normal: 

"The pectin is extracted with mineral acids such as nitric, hydrochloric or sulfuric acid, phosphoric acid and citric acid in an acidic aqueous medium."

That's from "Current Advancements in Pectin: Extraction, Properties and Multifunctional Applications", which I haven't read. All of those are mineral acids except citric, which is organic. I wouldn't be surprised if you can just use any acid, provided you get a low enough pH.

"Extraction process of pectin is carried out under reflux using acidified water at 97°C for 30 min. The hot acid extract was then filtered using a cheese cloth to remove the pulp. The filtrate was then cooled to 4°C and precipitated using double the volume of ethanol."

That's from "Extraction and Purification of Pectin from Agro-Industrial Wastes", which I haven't read. If you're refluxing a liquid but not removing a component by condensing, that's better known as boiling. So you boil pectin-containing plant matter with acid and then filter out the pulp. Next, cool the liquid and add ethanol to precipitate. The ethanol acts as an anti-solvent since pectin is a polar polysaccharide (the carboxyl groups can be protonated or deprotonated) that's well-dissolved by polar solvents, while ethanol is less polar than water. 

A few studies have found that pH around 3.5 is good for precipitating the most pectin across different circumstances. A pH between 2 and 3.5 is also needed in order for pectin to gel sugar, which is why SureJell brand pectin comes preloaded with sugar and citric acid.

I hear that reducing the water content before adding ethanol means you have to add less ethanol, so maybe boiling the plant material for longer has economic merit.

The precipitated pectin is a lump of jelly. Washing a few times over a filter with neutral or acidified ethanol will improve the purity. The pectin can then be dried and ground to a powder if you like, although drying might reduce the pectin "jelly-grade" a little, which is the number of grams of sugar that a gram of pectin and gel. It's a big deal in manufacturing to find slight modifications of production steps to retain a high jelly grade, but I don't have specific tips for you on how to do that.

Anyway: we've been talking about boiling with acid and precipitating with ethanol. But Henri Braconnot boiled with acid and then precipitated with potash, an alkali. Does that work too? Did he precipitate something different?

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