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.
...
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.
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