REPORT OF THE MICROSCOPIST. 141 



N"ow place a mouiited slide of fresh, butter, free from salt, over and 

 in contact with tlie selenite, and you see the same green color. These 

 experiments go to show that polarized light in passing through pure 

 oil and butter does not sutfer depolarization. If %e now combine a 

 few particles of tallow with oil or butter, and mount the specimen 

 with a glass cover in the usual way, every particle of tallow will ex- 

 hibit prismatic colors, the butter or oil being represented by the pure 

 green color. In this illustration lies the foundation of my method 

 of distinguishing butter from oleomargarine or other butter substi- 

 tutes. 



CRYSTALLINE FORMATIONS OF BUTTER. 



In earlier papers I have stated that if fresh butter is boiled, strained, 

 and cooled slowly, at a temperature of about G0° F. , mounted in the 

 usual way, and viewed by polarized light, crystals will be seen, as 

 represented by Figs. 1 to 4, inclusive, Plate I. 



Butter which has been improperly kept, subjected alternately to 

 high and low temperatures, will, if treated as above, show crystals 

 represented by Figs. 5 to 8, inclusive, same plate. If kept for a longer 

 period, say from two to three months, stellate crystals appear, which 

 m turn change during the process of fermentation to amorphous. 



These varied transitions can only be observed by keeping on hand 

 the original samples for a long period of time. 



CRYSTALS OF FATS. 



In preparing animal and vegetable fats for the purpose of develop- 

 ing their normal crystals their natural consistency must be consid- 

 ered. Some fats contain a much larger proportion of olein than 

 others, that of fish, fowl, and swine, for instance, while the fat of the 

 ox, sheep, and deer contains a smaller proportion of olein. The first 

 named may be rendered, cooled, and examined without the addition 

 of oil. The last mentioned will require oil to bring them to the con- 

 sistency of butter. For this purpose I use pure cotton-seed oil. It 

 is always desirable to simmer fats slowly, as by so doing they are not 

 so liable to scorch. If cooled at a temperature of about 60° F. for 

 about ten hours a perfect crystallization results. If quickly cooled, 

 say at a temperature of about 32° F. , the crystals will not form prop- 

 erly, and in some cases will not be observed. 



HOW TO MOUNT CRYSTALS OF FATS. 



Describe a varnish ring, by means of a turn-table, using copal or 

 other varnish. In the center of this ring place some lard in quan- 

 tity about the size of a small pin's head. Place over this a corre- 

 sponding amount of cotton-seed oil, mix with a point, place a cover, 

 corresponding in diameter with that of the ring,^over and in contact 

 with the soft varnish, and press gently. The specimen may thus be 

 viewed by plain or polarized light. Other fats having very small 

 crystals may be mounted in this way. Globose crystals of butter or 

 of other fats of large diameter require deep rings of a permanent 

 character. 



Owing to a diversity in the size of butter crystals and the crystals 

 of other animal fats, I have found it necessary to use powers varying 

 from fifty to five hundred diameters. 



