BUTTER AND OILS. ] 



CHEMISTRY. 



355 



between differently mixed blood and differently feeling 

 nerves, is perspicuous and evident. 



79. Butter and_0live Oil. In milk left undisturbed 

 for some time, cells containing butter rise to the surface. 

 From the stratum thus produced, by beating or stirring al 

 a higher temperature, butter is formed. The force ol 

 stirring, supported by a moderate heat, causes the cells 

 in which the butter has been included to burst ; the dis- 

 engaged fat collects into flakes, conglomerating into 

 larger masses. 



This origin explains why butter cannot consist of 

 pure fat ; the proportion of the fat in it does not 

 amount to more than from six-sevenths to four-fifths 

 of the whole, one-seventh to one-fifth consisting of 

 water combined with some caseine and sugar of milk. 

 The fat of the butter, however, is for the greater part 

 real butter-fat, or butyrine. By this name the chemist 

 designates a fat peculiar to butter, which, for a long 

 time, was supposed to be the only one present in it ; but 

 at the most, this amounts to but two-hundredths of its 

 weight. Butyrine becomes liquid at a very low tem- 

 perature. It consists of glycerine and butyric acid, 

 which is volatile in a free state, and possesses strongly 

 the characteristic odour of butter. Three fatty acids 

 besides, all volatile in an uncombined state, are, like 

 butyric acid, united with glycerine, and therefore with- 

 out odour in the fresh butter namely, the caseic, 

 sudoric, and capric acids. 



ther fats of butter are oleine and margarine. 

 As oleine is more fluid than the oil of almonds, the 

 solidity of butter depends exclusively upon the mar- 

 garine. At a very low temperature the oleine coagu- 

 lates, and accordingly produces the greater firmness of 

 butter in winter ; which is also partly to be explained 

 by the fact, that in the latter, oleine and margarine are 

 contained in the proportion of one to three ; while in 

 the butter made in summer, the inverse proportion 

 exists. Margarine melts at the temperature of 118 

 F;ih., and therefore winter butter aho liquefies at a 

 higher temperature. But while melted butter is cooling 

 again, the liquid fats separate from the coagulating mar- 

 garine, and hence the butter assumes a taste disagree- 

 able to most persons. But much more so is the decom- 

 position of real butyrine, and the other neutral fats 

 composed of the volatile acids and of glycerine ; for if 

 butyric, caseic, sudoric, and capric acids become dis- 

 engaged, the butter assumes an offensive, pungent odour, 

 and an acid taste, liked only by the Icelanders. The 



is then called rancid. 



This decomposition is produced by the caseine and 

 the water of the butter. Common salt, intermingled 

 with butter, has the advantage of attracting the water 

 and causing the caseine to be ineffectual ; while by the 

 process of melting, the caseine is skimmed off from the 

 surface of the butter as a gray scum, and the water 

 evaporates. For preservation, therefore, butter is gene- 

 rally melted and salted. 



Olive-oil is commonly used, as a condiment with salad. 

 It contains nearly three-fourths of oleine, and very little 

 more than one-fourth of margarine. In the oil of 

 almonds, the oleine is more than three-fourths, and the 



rine rather less than a quarter, of the whole. 

 Although these oils do not afl'ord any neutral fat 

 with volatile acids, yet they have the property of be- 

 coming rancid like butter ; for, by the process of de- 

 composition, both cascie and caprie acids are formed out 

 of oleic acid. This transformation, however, caused by 

 the influence of oxygen, takes place only very slowly in 

 olive-oil, as consisting entirely of mere fat ; and olive- 

 oil, as well as the oil of almonds, may be preserved for 

 a very long time without becoming in the least rancid. 



$ 80. DvgettOnUty of the Fat*. (My that small pro- 

 portion of the fats which can be saponified by the alkali 

 of the bile, the pancreatic and intestinal juices, is to be 

 considered soluble in the digestive juices. By far the 

 larger part is so finely suhidividcd by the pancreatic 

 juice and the bile, as to be able to penetrate the walls of 

 the lacteals and the veins. Moreover, with respect to 

 this fact, the fats are to be considered as difficult of 



digestion; they are far inferior to the constituents of 

 fat in the capability of being dissolved, but superior to 

 them in the greater conformity with the actual consti- 

 tuents of the blood. 



The observation, however, which was made a little 

 time ago, that starch is much more easily transformed 

 into fat if taken with some fat than if alone, proves 

 butter, as well as olive-oil, to be particularly useful. In 

 bread-and-butter, therefore, we have the satisfaction of 

 discovering a fresh and striking illustration of the truth, 

 that ancient experience often leaves to science nothing 

 to do but to establish and explain its laws . 



Quite unjustly, therefore, are butter and oil said, 

 without qualification, to be difficult of digestion ; and 

 the poor man has adopted the best substitute when ho 

 tries to supply the want of butter by grease. Butter 

 on bread is a necessity recognised by impartial science ; 

 salad without oil is digestible only by herbivorous 

 animals. 



81. Cheese. Cream, milk, skimmed milk, and whey 

 furnish severally cream-cheese, rich, meagre, and green 

 cheese. In its abundance of fat, cream-cheese is the 

 richest : while green cheese, prepared from whey, which 

 contains only a very small proportion of fat, is the 

 poorest of all. 



The principal constituent of cheese is the caseine of 

 the milk ; according to the means by which this caseine 

 has been coagulated, whether by rennet or by the lactic 

 acid formed in the milk itself, the cheese is called sweet 

 or sour-milk cheese. The action of the rennet (i.e., the 

 stomach of calves) is aided by a warm temperature ; a 

 high temperature causes cheese to become hard, just 

 as the abundance of fat makes cream-cheese soft. 



In milk, the fat closely adheres to the caseine ; in 

 cheese, therefore, the proportion of fat exactly cor- 

 responds with the relative quantity of butter. In addi- 

 tion to butter, the salts of the milk, and a part of the 

 sugar of milk, are to be found in cheese. In real 

 cheese the caseine and the butter are partly decomposed. 

 Of the caseine is formed a nitrogenised substance, the 

 "leacin," which we will denominate "cheese- white," as 

 it crystallises in glittering white threads, and as this 

 word recalls the chemical technical expression. Besides 

 ;his substance, an oily acid is developed, not very readily 

 soluble in water, which corresponds with the peculiar 

 acid of the root of valerian, not only by ita penetrating 

 odour, and its strong, pungent taste, but also in its com- 

 position and all other qualities; it is therefore called 

 valerianic acid. Some butyric acid besides is formed 

 of the caseine; and hence we find in cheese which is 

 several months old, more butyric acid than in fresh. 



But the greatest proportion of the butyric acid ori- 

 jinates from the decomposing butyrine ; and the same 

 a the case with the c;iseic, sudoric, and capric acids, 

 associated in cheese with the valerianic acid. 



A part of the whey is very often retained in the 

 cheese ; the sugar of milk of the whey is decomposed 

 nto butyric and carbonic acids, and the latter causes 

 ;ho holes to be observed in the Swiss and American 

 cheese. 



The odour and taste of the cheese is produced by the 

 r atty acids, as well as by the valerianic, which is similar 

 ,o them. Common salt decisively checks the formation 

 of these acids from caseine and butter. The taste of 

 many Dutch cheeses is less aromatic, from their being 

 mixed with an abundant proportion of common salt ; 

 and as the decomposition of caseino and butter increases 

 vitli their age, the odour and taste of the cheese is 

 much stronger the longer it has been kept. 



Though butyric acid may originate from three dif- 

 'ereut substances of the milk namely, from butter, 

 sugar, and caseine yet the butter contributes by far the 

 [reatest proportion of volatile acids. A rich cheese, 

 ike that of Limburg, smells therefore much stronger 

 ,han the poor Marzaliuo, or the still poorer green cheese. 



82. Digestibility of Cheese. In speaking of the fat 

 contained in confectionery, we have already remarked, 

 ,hat the digestion of it is the more difficult in propor- 

 ion as it has been transformed by a high temperature 



