116 JOURNAL OF THE [April, 



glass chimney the best. I use the " Harvard burner," with a 

 tin reservoir for the oil, six inches in diameter by about two 

 inches in depth. I would remark, by the way, that the crystals 

 appear much better by lamp-light than by day-light. 



For a vessel, in which to heat and dissolve the substances, I 

 find a small chemical flask, of two fluid ounces capacity, the 

 most convenient, as it can be held over the lamp by grasping 

 the neck with forceps, of which I find steel, artery forceps, of 

 five inches length, the best. One advantage of the flask is that 

 it does not lose the contained liquid very rapidly by evapora- 

 tion. The forceps will also be needed for holding the glass slip, 

 and the thin glass cover. 



A block of cast-iron, five by eight by two inches, with one 

 side planed, is used for the rapid cooling of the preparations. 

 Glass slips, thin covers and Canada balsam will suggest them- 

 selves. 



Salicin is soluble in 5.6 parts cold, and very largely in boiling 

 water. The crystals deposited from a solution by cooling are 

 in the form of needles, and frequently stellate groups appear, 

 even under these circumstances. But to get the finest crystalline 

 formations of this substance, I use the following method : — 



First, prepare in the little flask, before mentioned, a solution 

 in hot distilled water. The best results are obtained with a 

 solution somewhat below the point of saturation. Add a trace 

 of clean, pure gum-arabic, pulverized, a piece as large as a 

 moderate sized grain of wheat, to each one-half fluid ounce of 

 the solution. The use of the gum is to retard the formation of 

 the crystals, and thereby enable the operator to obtain much 

 better results. If, however, too much gum is added, persistent 

 bubbles will be formed in the deposit on the slide. 



Next filter the hot solution, being careful that funnel, flask, 

 etc., are clean, and free from all traces of oily matter. 



To prepare the slide, which first must be made clean, hold the 

 slip in the forceps by one end ; warm over the lamp ; remove, 

 and pour on the end, opposite the forceps, enough of the hot 

 solution to flow over as much of the slide as possible, and not 

 come in contact with the forceps, being very careful not to allow 

 any of the solution to run over. Now heat the slide over the 

 lamp, mostly at the end opposite to that held by the forceps, 

 causing some boiling ; and then, by slight motion of the slide, 



