M I I.
MIL
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t'hofe of Meffrs. Fourcroy and Vauquelin, ' thecoagulum thus formed confifts of the curd unitedwith a portion of the acid employed, infomuchthat if no more acid be ufed than is barelynecefhiry, the whey {hews no marks of acidity.The curd obtained by mineral acids (accordingto Scheele ) is foluble in an excels of the acid,but not that produced by vegetable acids. If milkbe previoully mixed with ten parts of water, nocurd is obtained by mineral acids, hence thecaufe of coagulation of undiluted milk in thiscal'e is, that the curd and acid together form acompound which requires for its folution muchmore water than the milk contains.
When milk is kept in a warm place it isknown to grow four and thick in about twodays, according to the temperature. This four-nefs daily increafes, and is the ftrongeft whenabout a fortnight has elapfed, and it then confiftsof a fort curd, acid and fomewhat naufeous tothe tafte, and of whey highly four and whitifh.A ftrong acid is therefore generated in the pro-cefs which was firft accurately examined byScheele , who difcovered that the acid differedfrom any other then known, and to which hegave the name of LaBic Acid. It was thusprepared by this excellent chemift : the fourwhey was filtered and evaporated till only one-eighth remained. Some curd was feparated inthe procefs, which being removed by filtrationthe. acid liquor was faturated with lime-water,by which a white precipitate of phofphat oflime fell down and was removed. To the clearliquor (confifting of the peculiar acid and limeand fomc mucilaginous matter) juft enough ofoxalic acid was added to engage and precipi-tate the lime, which left the acid of the milkfree in the liquor. This was then evaporatedto the confiftence of honey, and ftrong alcoholadded, which diffolved only the acid, leavingbehind the iugar of milk and other fubftancescontained in the whey. The alcoholic folutionwas then diluted with water, and the alcoholdiftilled oft', which finally left the laftic acidin a liquid ftate in the retort as pure as it canever be obtained.
The labtic acid is deferibed by Scheele tohave the following properties : evaporated to athick confiftence it gives no cryftals, and whendried it readily ddiquefces again ; when diftil-led it yields water, a weak acid like the tarta-rcous, and afterwards empyreumatic oil, acid,and an inflammable air: faturated with potafhit gives a cleliquefcent fait, foluble in alcohol,and with foda an uncryftallizable fait, but alfo
foluble in alcohol. With ammonia and theearths it forms deliquefcent falts. It difl’olves•iron and zinc, giving out inflammable air, anda£ts upon fome of the other metals.
It cannot be formed direftly from four wheyby diftillation, for on making the trial, only aflightly acidulous water rifes in a boiling heat,and by far the greater part of the acid remainsbehind in the retort. From its very clofe re-femblance to vinegar, the difeoverer confidersit as an imperfedh acetous acid, containing thematerials of this acid, but wanting the vinousfermentation to be compleatly elaborated. Inproof of this opinion he adds, that if to akanne (lb 5^ Englifh) of milk be, added fouror five fpoonfuls of brandy, and the veflel con-taining it, well corked, be expofed to warmth■with occafional exit of the vapour generated,the whole of the whey will be changed intogood vinegar.
Some later experiments have "been made byMeffrs. Fourcroy and Vauquelin , on fouredmilk, particularly with a view to determine theexa£I nature of Scheele ’s la&ic acid, wherebyit appears moft probable that this acid is in fadhacetous acid, but with its perfect characterfomewhat maiked by holding in folution a quan-tity of animal matter. We fliall in a few wordsgive the leading particulars of thefe valuableexperiments, as they alfo throw fome furtherlight on the general analyfis of milk.
A quantity of milk was let to ftand in a warmplace for five days till it was quite four, afterwhich the cream was carefully Ikimmed off andthe remainder was heated to compleat the repa-ration of the curd from the whey. The curdwell wafhed and prefled dried into a flexibletnvnfparent horny fubftance, which when burntto allies left a finall quantity of afli (much lefsthan when the curd is prepared from fweet milkby rennet) moft of which was phofphat of lime.
The four whey was then carefully analyzedin the following manner. Lime-water wasadded as long as any precipitate fell down,which latter was collected and calcined, duringwhich it gave out ammoniacal oily vapoui>s,Ihewing the prefence of an animal matter. Thecalcined refidue treated with fulphuric acid gavefulphat of lime, and phofphoric acid was foundill the fupernatant liquor. ^ By evaporation ofthis laft to drynefs and calcination, the refidueaffumed a red colour, and on adding water partwas diftolved and a red oxyd of iron was left;The folution depoflted by reft fome cryftals offulphat of magneha. Hence it appeal that the