Equipped with a good microscope, the analyst should obtain a fair supply of typical slides for comparison. The following selection will be found sufficient for his purpose: A set of the chief varieties of uric acid, calcic oxalate, and triple phosphate; the urates and oxalurates; urea nitrate, calcic hippurate and carbonate, hippuric acid, cystin, well mounted "casts" of the _tubili uriniferi_, spermatozoa, etc. In doubtful cases microchemical reagents can be employed, using Professor Attfield's "Chemistry" as a guide. Where mounted objects are not at hand, reference may be made to the capitally executed plates in that work. After obtaining a little experience in the use of the microscope, no difficulty will be met with in these examinations.--_The Chemist and Druggist._ * * * * * LIQUID AND GASEOUS RINGS. All who have learned a little of chemistry doubtless remember the experiment with vortex rings produced by phosphorus trihydride mixed with a little phosphide of hydrogen. As this curious phenomenon evidently does not depend upon the peculiar properties of this gas, I have been trying for some time to reproduce it by means of tobacco smoke, and even with chemical precipitates, which are, in a way, liquid smoke. After a few tentatives made at different times, my experiment succeeded perfectly. The following is, in brief, the mode of operating: Take up a little hydrochloric acid in a pipette and put a few drops of it into a very dilute solution of nitrate of mercury, and you will obtain rings of mercurial chloride that will, in their descent, take on the same whirling motion that characterizes the aureolas of phosphureted hydrogen. The drops of acid should be allowed to fall slowly, and from a feeble height, to the surface of the liquid contained in the vessel. It is unnecessary to say that the result may be obtained through the use of other solutions, provided that a precipitate is produced that is not very thick, for in the latter case the rings do not form. If need be, we may have recourse to milk, and carefully pour a few drops of it into a glass of water. [Illustration: FIG. 1.--PRODUCTION OF SMOKE RINGS.]