M I L.

M I L

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and tranfparcnt like horn, which may be feen infome of the mofl ordinary cheefes as preparedfor food. Whilft it retains its flexibility it isextremely tough and tenacious, and whenheated it draws out into long firings. If theheat becomes fcorching it melts, takes fire andburns with flame, fmoke, and a fetid ammonia-cal fmell. When diftilled perfe it alfo yieldsmuch ammonia, a fetid oil, much' fulphurettedand carburetted hydrogen, and a denie falinecoal from which muriat of potalh may be ob-tained by lixiviation. Curd alfo contains muchof the phofphat of lime of the milk, providedthe milk has not flood long enough to four andgenerate an acid which would keep this earthyfait fufpended. And, when dry and horny, itwill keep to an indefinite time in a dry air with-out change, but if foft and not well prefled,the whey which it contains becomes four, anddie acid itfelf in a few days is covered with awhite mould, gives out a mofl offenfive fmell,and flowly putrefies. But the fpontaneous de-compofition of cheefe is very flow.

Curd is infoluble in water, but when longkept under cold water,, it is changed to a foftfatty matter, considerably different from theoriginal fubftance. Csuflic alkali diffolves curdvery readily, particularly if heated, and it maybe again precipitated by acids. Some ammoniais difengaged during the folution. Ammoniaalfo a£ls on curd with equal rapidity. Quick-lime, curds and water, intimately united bybeating, form a ftiffpafte of extreme tenacity,which foon acquires a ftrong hardnefs and isoften ufed as a very firm cement.

From all the properties of pure curd itappears to bear the ftrongeft analogy with thewhite of egg, as Scheele obferves, and it maybe confidered as nearly pure albumen, butmixed with a certain portion of phofphat oflime and a few other laline matters. Rouelle.compared it to the gluten of wheat, which isalfo a juft comparifon, fince there is alfo fcarcelyany afcertainable difference between pure glutenand pure albumen when each is in a condenfedcoagulated flate. The effe£l of acids upon curdwill be preiently noticed.

Butter, or the oily part of milk, is well-knownto be prepared from cream by long agitation.New milk is perfectly homogenous, but onHanding for fome hours at reft it throws up' athick yellowifh-white cream, unfituous to thetouch, and of a very bland agreeable flavour.In the pjocefs of churning, the cream feparatesvifibly into two. fubflances, the butter whichcolletfts in a mats, and a thick white liquid, the

buttermilk as it is called, and whey, and Hillretains a little of the butter.

Butter is much more eafily made from flalethan from frefli cream, probably owing to thefpontaneous change which cream undergoes bykeeping, and the evolution of an acid. Butteroften varies in colour, being of every fhade froma faint yellowifh-white to a deep yellow, but thecaufe of this variation is not very apparent.The a£lion of the atmofphere has been thoughtby fome to be concerned in the feparation of,cream from milk, and of butter from cream,but nothing in the leaft degree fatisfadlory hasbeen brought in fupport of this opinion, and itis certain that agitation alone in a corked bottle,will perfedlly feparate butter from cream.

Frefli butter melts at about 98°, and whenkept for fome time melted, a fmall quantity of.ferurn and curd feparate from it. The butterbecomes- thereby more tranfparent, but has ac-quired a lefs pleafant tafte. Butter when diftilledper fe , firft gives over fome water bolding fe-bacic acid, after which the greater part of thebutter rifes with a pungent unpleafant fmell,and fixes in the receiver into a concrete-empyreu-matic greafe. A further diftillation of this greafegives a finer and more volatile oil than at firfl,and other products fimilar to thofe of the animaloils, as will be further mentioned under thearticle Oil. Butter when long kept becomesexceffively fetid and rancid, but this is in agreat meafure prevented by falting. Alkaliesdiflblve it with eafe into a perfeil foap.

On the whole, butter may be confidered asmofl refembling the animal oils, but intimatelycombined with a fmall portion of the curd andwhey and other parts of the milk, from whichprobably it can never be feparated without totaldiforganization; and indeed as miik is a natu-ral emulfion elaborated in the veflels of theanimal, the combination of its parts appearsthroughout to be fo clofe that it is fcarcely in thepower of art to break it iivtireiy. Hence it is thatwe find the whey to retain almofl to the laflfome of the curd and oil; the curd to be almoflinfeparable from tlie lafl portions of the whey andbutter (to which much of the varieties of cheefeis to be attributed) and fome of the curd amiwhey to remain in the compofition of. butterthrough every procefs.

We proceed , to deferibe the efte£l of, acidsupon milk, and the fpontaneous coagulation ofmilk by the acid which is generated in it bykeeping for a certain length of time.

All acids readily curdle milk, and as appearsfrom the experiments of Scheele, confirmed by