Principles and practice of agricultural analysis; a manual for the study of soils, fertilizers, and agricultural products for the use of analysists, ... students of agricultural chemistry Volume 3

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1914 edition. Excerpt: ...and these lards may have been made partly of cotton oil stearin. When a lard crystal presents its edge to observation it may readily escape identification, or may even be mistaken for a crystal of beef fat. In order to insure a side view the cover glass should be pressed down with a slight rotatory movement,' whereby some of the lard crystals at least may be made to present a side view. 333. Observation of Fat Crystals with Polarized Light.--The appearance of fat crystals, when observed by means of polarized 55 Division of Chemistry, Bulletin 13, Part 1, 1887: 452, 29 et seq. light alone or with the adjunct of a selenite plate, is often of value in distinguishing the nature and origin of the sample.56 Every fat and oil which is amorphous will present the same set of phenomena when observed with polarized light through a selenite plate, but when a fat has been melted and allowed to cool slowly the field of vision will appear mottled and particolored when thus examined. This method has been largely used in the technical examination of butter for adulterants, and the microscope is extensively employed by the chemists of the Bureau of Internal Revenue for this purpose. In the examination of the crystals of butter fat by polarized light a cross is usually observed when the nicols are turned at the proper angle, but the cross, while almost uniformly seen with butter, is not distinctive, since other fats often show it. These forms of crystals are best obtained by heating the butter fat to the boiling-point of water for about a minute and then allowing it to slowly solidify, and stand for 24 hours. Pure butter, properly made, is never subjected to fusion, and hence, when examined through a selenite plate, presents a uniform field of vision similarly...