Conversations on Chemistry Part 111

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This is a very useful piece of information; for I find white-wine whey, which I sometimes take when I have a cold, extremely heating; now, if the whey were separated by means of an alkali instead of wine, it would not produce that effect.


Perhaps not. But I would strenuously advise you not to place too much reliance on your slight chemical knowledge in medical matters. I do not know why whey is not separated from curd by rennet, or by an alkali, for the purpose which you mention; but I strongly suspect that there must be some good reason why the preparation by means of wine is generally preferred. I can, however, safely point out to you a method of obtaining whey without either alkali, rennet, or wine; it is by subst.i.tuting lemon juice, a very small quant.i.ty of which will separate it from the curds.

Whey, as an article of diet, is very wholesome, being remarkable light of digestion. But its effect, taken medicinally, is chiefly, I believe, to excite perspiration, by being drunk warm on going to bed.

From whey a substance may be obtained in crystals by evaporation, called _sugar of milk_. This substance is sweet to the taste, and in its composition is so a.n.a.logous to common sugar, that it is susceptible of undergoing the vinous fermentation.


Why then is not wine, or alcohol, made from whey?


The quant.i.ty of sugar contained in milk is so trifling, that it can hardly answer that purpose. I have heard of only one instance of its being used for the production of a spirituous liquor, and this is by the Tartan Arabs; their abundance of horses, as well as their scarcity of fruits, has introduced the fermentation of mares' milk, by which they produce a liquor called _koumiss_. Whey is likewise susceptible of being acidified by combining with oxygen from the atmosphere. It then produces the _lactic acid_, which you may recollect is mentioned amongst the animal acids, as the acid of milk.

Let us now see what are the properties of curds.


I know that they are made into cheese; but I have heard that for that purpose they are separated from the whey by rennet, and yet this you have just told us is not the method of obtaining pure curds?


Nor are pure curds so well adapted for the formation of cheese. For the nature and flavour of the cheese depend, in a great measure, upon the cream or oily matter which is left in the curds; so that if every particle of cream be removed from the curds, the cheese is scarcely eatable. Rich cheeses, such as cream and Stilton cheeses, derive their excellence from the quant.i.ty, as well as the quality, of the cream that enters into their composition.


I had no idea that milk was such an interesting compound. In many respects there appears to me to be a very striking a.n.a.logy between milk and the contents of an egg, both in respect to their nature and their use. They are, each of them, composed of the various substances necessary for the nourishment of the young animal, and equally destined for that purpose.


There is, however, a very essential difference. The young animal is formed, as well as nourished, by the contents of the egg-sh.e.l.l; whilst milk serves as nutriment to the suckling, only after it is born.

There are several peculiar animal substances which do not enter into the general enumeration of animal compounds, and which, however, deserve to be mentioned.

_Spermaceti_ is of this cla.s.s; it is a kind of oily substance obtained from the head of the whale, which, however, must undergo a certain preparation before it is in a fit state to be made into candles. It is not much more combustible than tallow, but it is pleasanter to burn, as it is less fusible and less greasy.

_Ambergris_ is another peculiar substance derived from a species of whale. It is, however, seldom obtained from the animal itself, but is generally found floating on the surface of the sea.

_Wax_, you know, is a concrete oil, the peculiar product of the bee, part of the const.i.tuents of which may probably be derived from flowers, but so prepared by the organs of the bee, and so mixed with its own substance, as to be decidedly an animal product. Bees' wax is naturally of a yellow colour, but it is bleached by long exposure to the atmosphere, or may be instantaneously whitened by the oxy-muriatic acid.

The combustion of wax is far more perfect than that of tallow, and consequently produces a greater quant.i.ty of light and heat.

_Lac_ is a substance very similar to wax in the manner of its formation; it is the product of an insect, which collects its ingredients from flowers, apparently for the purpose of protecting its eggs from injury.

It is formed into cells, fabricated with as much skill as those of the honey-comb, but differently arranged. The princ.i.p.al use of lac is in the manufacture of sealing-wax, and in making varnishes and lacquers.

_Musk_, _civet_, and _castor_, are other particular productions, from different species of quadrupeds. The two first are very powerful perfumes; the latter has a nauseous smell and taste, and is only used medicinally.


Is it from this substance that castor oil is obtained?


No. Far from it, for castor oil is a vegetable oil, expressed from the seeds of a particular plant; and has not the least resemblance to the medicinal substance obtained from the castor.

_Silk_ is a peculiar secretion of the silk-worm, with which it builds its nest or coc.o.o.n. This insect was originally brought to Europe from China. Silk, in its chemical nature, is very similar to the hair and wool of animals; whilst in the insect it is a fluid, which is coagulated, apparently by uniting with oxygen, as soon as it comes in contact with the air. The moth of the silk-worm ejects a liquor which appears to contain a particular acid, called _bombic_, the properties of which are but very little known.


Before we conclude the subject of the animal economy, shall we not learn by what steps dead animals return to their elementary state?


Animal matter, although the most complicated of all natural substances, returns to its elementary state by one single spontaneous process, the _putrid fermentation_. By this, the alb.u.men, fibrine, &c. are slowly reduced to the state of oxygen, hydrogen, nitrogen, and carbon; and thus the circle of changes through which these principles have pa.s.sed is finally completed. They first quitted their elementary form, or their combination with unorganised matter, to enter into the vegetable system.

Hence they were transmitted to the animal kingdom; and from this they return, again to their primitive simplicity, soon to re-enter the sphere of organised existence.

When all the circ.u.mstances necessary to produce fermentation do not take place, animal, like vegetable matter, is liable to a partial or imperfect decomposition, which converts it into a combustible substance very like spermaceti. I dare say that Caroline, who is so fond of a.n.a.logies, will consider this as a kind of animal bitumen.


And why should I not, since the processes which produce these substances are so similar?


There is, however, one considerable difference; the state of bitumen seems permanent, whilst that of animal substances, thus imperfectly decomposed, is only transient; and unless precautions be taken to preserve them in that state, a total dissolution infallibly ensues. This circ.u.mstance, of the occasional conversion of animal matter into a kind of spermaceti, is of late discovery. A manufacture has in consequence been established near Bristol, in which, by exposing the carcases of horses and other animals for a length of time under water, the muscular parts are converted into this spermaceti-like substance. The bones afterwards undergo a different process to produce hartshorn, or, more properly, ammonia, and phosphorus; and the skin is prepared for leather.

Thus art contrives to enlarge the sphere of useful purposes, for which the elements were intended by nature; and the productions of the several kingdoms are frequently arrested in their course, and variously modified, by human skill, which compels them to contribute, under new forms, to the necessities or luxuries of man.

But all that we enjoy, whether produced by the spontaneous operations of nature, or the ingenious efforts of art, proceed alike from the goodness of Providence. --To G.o.d alone man owes the admirable faculties which enable him to improve and modify the productions of nature, no less than those productions themselves. In contemplating the works of the creation, or studying the inventions of art, let us, therefore, never forget the Divine Source from which they proceed; and thus every acquisition of knowledge will prove a lesson of piety and virtue.

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Conversations on Chemistry Part 111 summary

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