M 1 L

M 11

( 100 )

juice of all animals alfo produces the fameefteft, and hence coagulation is the firft procefsin the natural digeftion of this fluid.

Coagulation is the moll convenient methodof analyzing milk, and it is thereby refolvedinto two principal portions, the coagulum orcurd, and the iuhey. The analyfis of each ofthefe fubftances gives the following refults.

Whey prepared by rennet (which is on thewhole the belt fubftance for coagulating milkfor chemical analyfis) when filtered and clarifiedis a limpid yellowifh fluid, of a fweetifh andrather faline tafte, agreeable to moll palates.Its fpecific gravity is fomewhat lefs than thatof the milk from which it is procured. Wheywhen gently evaporated to the confiftence of afyrup and allowed to cool undifturbed, depofitsa lingular crystalline fweetifh matter calledfugar of milk, which is prepared pretty largelyin fome of the Swifs cantons, and is ufed forculinary and medicinal purpofes. To prepareit, frefh whey from fkimmed milk is boileddown to the thicknefs of fyrup, and then pouredinto earthen pots, where it folidifies and driesin the fun; this mafs which is brown andimpure is refined by re-folution, clarificationwith white of egg, and another evaporation,after which it concretes into white rhomboidalcryftals.

Sugar of milk when pure is a white cryftallinefubftance, of a fweetifh and rather mawkifhtafte, foluble in four parts of boiling water andabout twelve of cold. When ftrongly heated itturns brown, fwells up and exhales the ftrongpungent vapour of burnt fugar, and finallyleaves a black coal holding about of itsweight of fait, compofed according to Rouelle,of three parts muriat of potafh and one partcarbonat of potafh.

Sugar of milk has been ufually thought to bethe chief agent in the vinous fermentation,which milk is capable of afluming, but it hasbeen fliewn by Fourcroy and Vauquelin thatthis is a miftake, fince during the procefs nofugar of milk is deftroyed, as much being found*ifter as before fermentation. Neither is itcapable of fermenting by itfelf when diflolvedin water and mixed'with leaven.

Sugar of milk when boiled with nitric acidrepeatedly, is converted partly into oxalic acidand partly into a peculiar arid to which theterm SaccholaSlic Acid, or Acid of Sugar of Milk,has been given. It was firft difeovered by theingenious refearches of Scheele, d and has fincebeen found to be identic with the mucous acid.

It is prepared by abftra&ing nitric acid repeat-edly from fugar of milk, during which an opakewhite powder feparates firft, and on cooling aquantity of cryftals alfo forms. The former isthe faccholadtic acid, the latter is oxalic acid.The faccholactic acid is very fparingly folublein hot water, and poflefies very faint acid pro-perties, but its arid nature cannot be doubtedfince it reddens litmus, has a flightly four tafte,effervefees with chalk, and forms neutral faltswith alkalies. It has been ftrongly fufpedledto be the oxalic acid, whofe ufual propertiesare mafked by an intimate union with fomeanimal matter, but no fatisfariory experimentshave confirmed this opinion. Its propertieswill be further noticed under the- articleMucous Acid.

After the evaporated whey has depofited all,its fugar of milk, the mother- liquor is a brownvifeous fluid, which on cooling concretes into-a tremulous jelly. It alfo contains moft of the’faline parts of the milk, which may be obtained'by diluting it with water and again evaporatingjudicioufly and flopping the procefs at intervalsto allow of the reparation of the falts. Themoft abundant of thefe is muriat of potafh,which appears in fmall regular cubic cryftals.Phofphat of lime is alfo contained in ferum andfeparates at laft, but it may be more immedi-ately obtained by adding lime-water to the wheybefore evaporation, this earthy fait bring there-by rendered infoluble, the lime-water neutral-izing a fmall excefs of acid naturally exifting inmilk which holds the phofphat in folution. Anyof the alkalies will produce the fame effe£t.The above two falts, muriat of potafh and phof-phat of lirne alfo appear, on calcining die dryrefidue of evaporated whey, and lixiviating withwater, the heat having deftroy,; 1 the acidwhich held the phofphat of lime fu (pended.

The phenomena attending the coagulation ofmilk by acids and by alcohol will be foon no-ticed, that by rennet is underftood at prefent.

The curd of milk prepared by rennet, to bechemically pure, fhould be made of flri'mmedmilk, otherwife it contains much of the butterand oily part. The -confiftence of curd dependson a number of minute circumftances, beingfometimes quite foft and gelatinous, fometimesfirm and as it were knotty, it is much con-denfed and hardened by heat. A long conti-nued preffure is neceffary, in order to feparateentirely the adhering portion of whey. Curd.(orcheefej from fkimmed milk, when flowlydried in a moderate heat, becomes hard, brittle,

4 Effayj.

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