BUTOMUS, a genus of plants of the class Ennt.an dri:, and of dt r Ilexagynia. lice Ilo'r NV, p. 201.
BuTTER, a fat unctuous substance, usually prepared from the cream of cows milk by agitation. It is of a yel low co;our, sometimes higher, sometimes lighter, pos sesses the properties of an oil, and readily mixes with other oily bodies. The process by NS 111C11 it is obtained from cream, is that sort of agitation called churning, well known to every body. When pure, it is soft and concrete, and of an agreeable sweet taste. It melts at the temperature of 96", and becomes transparent ; but if it be kept for some time in this state, a portion of curd and water, or whey, is disengaged, and it assumes exact the appearance of oil. It. has now, however, lost al most all its peculiar flavour.
Butter has been usually thought to be a matter natu rally distributed through the milk, and existing, along with the caseous and scrolls parts thereof, in a state of mechanical suspension, similar to that in which oil is, when suspended in water by means of syrup or muci lage. But though a mixture of this sort, commonly call ed an emulsion, puts on a white colour like milk, and its oily parts by rest rise to the top, and form a cream similar to the cream of milk, yet the experiments of Messrs. Deyeux and Parnientier seem to have proved, that butter does not actually exist in the cream, but that it is formed from it during the process of churning, by certain che mical changes which then occur. These gentlemen were led to form this opinion, by observing, that butter could not be produced in any other way' than by agitation ; be cause whatever substances or means they employed to detach either the cheesy or buttery part of the cream, they always found agitation or churning necessary.
Fourcrov considers the butyraceozza matter of milk as quite distinct from butter ; and says, it is a white liquid oil, suspended in the scrum, by means of the muco saccharine and cheesy' parts, which, combining with oxygen, forms butter. The oxygen he conceives it to obtain partly from the atmosphere, and partly from the milk itself. l le is of opinion, that butter in a small quan tity can he obtained without agitation ; and says, that the oily particles of the butyraccous matter, which, from their greater levity, float, when the milk is allowed to rest, on the surface of the cascous and serous fluid, absorb oxy gen from the atmosphere, and become real butter.
That important chemical changes take place during the operation of churning, there can be no doubt ; but the nature of these is still, we apprehend, imperfectly understood. Farther experiments seem necessary to elucidate the subject. In all cases, there is a considera ble extrication of gas ; and Dr Young affirms, that there is likewise a rise of temperature equal to four degrees. In the Mid-Lothian agricultural report for 1795, it is stated, that cream churned in contact with atmospheric air, absorbed a considerable quantity of it. But Dr Young has shewn, that butter may be obtained from cream by churning, without the contact of air. These two state ments, however, arc not irreconcileablc, since, according to Fourcroy, the butyraceous matter takes its oxygen partly from the air, and partly from the milk. That this matter should absorb oxygen, and thereby acquire the consistence of butter, is quite analogous to what happens to other oily bodies, which all become thicker by absorb ing the oxvgenous ptinciple. The gas disengaged is probably the carbcilic acid gas ; for every person must have obstrved, that whin even sour cream is churned, the butter uhtzined is pe:fettly sweet , and the milk re maining in the churn, fx.iled the butter-mill:, is always much less sour than the cream had been.
I- utter is o'-taintd usually' by agitating cream, it may be also cot by aL,it.,ting milk as di awn from the cow, ar.tl evt n in grt.itt r cualnity than from the citam alone the same milk : a fact \% ill known to those who superit tt nd dairies. Even wl cv. by churnin,, yiclt:s but ter. In the agricultural rt pert before quoted, it is stat ed, that 27 Scotch pints of whet. tLat about If 3 Eng lish, afford at an a \ lraZt. uric T.,.und of butter. The oily part of the milk appears to have so strong an attraction for the other ingredients, that it never completely sepa rates from them.