622 REPORT OF THE COMMISSIONER OF AGRICULTURE. 
useful owing to special properties, or the discovery of any new prop- 
erty characteristic of any fat or oil that would assist by contrast in the 
detection of artificially mixed fats or oils, whether used as food, med- 
icine, delicate lubricants, drying oils, or for other purposes. 
The solid fats of animals accustomed to great muscular exertion, 
such as the horse, winged animals, and some fishes, seem to contain, 
as far as my observations extend, a larger proportion of oil than is 
found in the solid fats of animals of more sedentary habits. 
The fats of consumptives, whether of man or the lower animals, 
victims of exhausting fevers, exhibit like conditions. Thus in the 
production of abnormal heat in the animal economy, whether arising 
from chemical or muscular energy, the result seems to be the same. 
The solid fats seem to be more readily consumed than the oil. 
LARD EXAMINATION. 
Agreeably to your request I have made a special examination of 
about 100 samples of lards, pure and adulterated, not only with the 
microscope, but by means of the color-reactions’ test with sulphuric 
acid. sue eae 
The result of my examination shows that nearly all of the samples 
were Coa lease of lard, cotton-seed oil, and beef-fat stearin. 
The following apparatus and re-agents were employed: 
Plate 4, Fig. 1, spatula (one-quarter size). Fig. 2, inverted saucer (full size). Fig. 
3, porcelain mortar and pestle of any convenient size. Fig. 4, sulphuric acid, C. P.,. 
specific gravity 1.705. Fig. 5, graduated tube. Fig. 6, a test tube. 
The lard oil is measured in Fig. 2, and in case of the former, 
smoothed evenly to the rim by meansof the spatula. Transfer the fat 
or oil thus measured to the mortar, fill the graduated measure one- 
quarter full of sulphuric acid, and pour it on the fat in the mortar. 
Triturate the fat and acid for one minute and add a sufficient quan- 
tity of acid to fill the test tube into which the contents of the mortar 
are emptied two-thirds full and let it settle. In the case of mixed 
fats the sulphuric acid sometimes appears of a yellow or red shade 
in the lower part of the tube. 
FLUORESCENCE: 
It has been held heretofore that the fixed fats and oils are not 
fluorescent. (See Alfred H. Allen’s Commercial Organic Analysis; 
vol. 2, p. 1, 1886.) ; 
It may be well to explain for the general reader that by the term 
‘fixed’ fats and oils is meant those which make a greasy stain on 
paper, not removable by heat without destroying the paper. Hssen- 
tial oils are not oleaginous to the touch and make no permanent 
grease spot. In chemical constitution they present no relationship 
to the fats and oils. The stain of the essential oils may be readily 
removed at a temperature of 212° F. 
Fluorescence is a term used by Professor Stokes in explanation of 
the phenomena called by Sir J. Herschel epipolic dispersion, and_by 
Sir D. Brewster internal dispersion. Professor Stokes found that 
on examining the light produced by the solar spectrum falling upon 
a fluorescent substance it possessed a less refrangibility than the in- 
cident rays, and he was therefore led to the discovery of the change 
of the refrangibility of the rays of light, the highly refrangible ac- 
tinic rays being degraded into luminous rays of less refrangibility. 
