182 Extracts from Report on the Analysis of Butter. 
result had been arrived at ; in fact, the results were rather 
misleading than otherwise. 
In applying the specific gravity test to butter, the curd, salt, 
and water are first removed, and the density of the melted fat 
at 100° Fahr. is taken in an ordinary specific-gravity bottle. 
The bottle used for the purpose was of a pear shape, into which 
could be inserted the bulb of a sensitive thermometer, the 
mercurial portion of which extended nearly the whole depth of 
the bottle. The temperature of 100° Fahr. was adopted, as at 
that temperature nearly all the animal and vegetable fats likely 
to be used as butter adulterants assume the liquid state. 
It will be seen from Table I. that the specific gravity of 
ordinary animal fats varies from 902 - 83 to 904 - 56, while the 
Table I. Kksdlts of Analyses of Animal Fats. 
Description of Sample. 
Specific 
Gravity at 
100° Fahr. 
Percentage 
of fixed 
Fatty Acids. 
902-83 
95-86 
903-72 
95-91 
903-84 
96-20 
901-56 
94-67 
Mutton Dripping (Genuine) .. 
903-97 
95-48 
specific gravity of butter fat, as exhibited in Table II. (p. 184 
et seq.), rarely falls below 910", the usual range being from about 
911* to 913*. There is thus a material difference between the 
specific gravity of butter fat and that of ordinary commercial 
animal fats, and it is obvious that this difference affords a satis- 
factory basis upon which to found an additional test for deter- 
mining the purity of butter. 
It may be useful to describe here briefly the difference between 
the composition of ordinary animal fats and that of butter fat. 
The former consist of a mixture of stearic, palmitic, and oleic 
acids, in combination with glycerine, and as these acids are 
insoluble in water, and not readily volatilized, they are com- 
monly called " fixed " fatty acids, in contradistinction to other 
fatty acids which are either volatile or soluble in water, such as 
butyric, caproic, caprylic, &c, acids. Butter fat also consists 
of fatty acids in combination with glycerine, but while by far the 
larger proportion of the acids are of a " fixed " nature, there are 
invariably present several of those which are volatile or soluble 
in water, and it is to the latter, the most important of which is 
butyric acid, that the characteristic taste and smell of butter are 
