5-] 



MICROSCOnCAL JOURNAL. 



153 



of crystals, but to describe, in as 

 simple a manner as possible, how I 

 have produced and how you may prob- 

 ably produce interesting, beautiful, 

 and valuable microscopical slides of 

 some of these wonderful forms. 



In describing the mode of prepara- 

 tion of some of the micro-crystals, 

 those which are most readily prepared 

 have been selected, — one of the 

 easiest being tartaric acid ; this, like 

 many others of the common objects 

 of the microscope, is very beautiful, 

 and is thus prepared : — 



Make a strong solution in water of 

 the acid crystals, and having warmed 

 a slide, drop on the centre a little of 

 the solution and evaporate by gentle 

 heat, that is by holding the slide some 

 four or five inches above the flame of 

 the spirit lamp. If only a small drop 

 of the solution has been used, the 

 crystals will be thin, and will require 

 a selenite to bring out their utmost 

 beauty ; but if the drop of solution is 

 heaped up, as it were, on the slide, 

 the crystallization will be stronger and 

 will not need the selenite, but as the 

 polarizer is rotated, the color will be 

 well shown. 



Immediately following this, may be 

 mentioned gallic acid, of which a 

 moderately strong solution is to be 

 made in methylated spirit. Drop a 

 little of this solution in the centre of 

 the cold slide and allow to evaporate 

 very slowly ; if, however, smaller crys- 

 tals are desired, as soon as the slight- 

 est appearance of crystallization is 

 visible, slightly, very slightly, warm 

 the slide. A third and different form 

 of crystal is obtained by adding to- 

 gether saturated solutions of the acid, 

 both in water and methylated spirits ; 

 then placing a little of the mixture on 

 the centre of the warm slide, and as 

 soon as the crystals commence to form, 

 pricking the centre with a cold needle. 



The preparation of the slides from 

 these two acids separately, naturally 

 at this point leads me to notice a form 

 of crystal obtainable by a mixture of 

 the two as follows : — 



Make a strong solution of each in 



methylated spirits, and then, mixing 

 both together, place a drop upon a 

 cold slide, gently warm until opal, 

 oyster shell-like crystals begin to ap- 

 pear; instantly then remove from the 

 warmth, and generally the appearance 

 of the slide is improved if now it is 

 cooled rapidly by placing it upon a 

 cold surface ; but this is a matter re- 

 quiring more attention and experiment 

 than has yet been given to it, and 

 though I cannot always depend upon 

 getting this precise form, when ob- 

 tained, they are very interesting, 

 showing a combination of the broad 

 crystallization of the tartaric, and the 

 needle-like crystals of the gallic acid. 

 This combination when produced 

 needed a name, and upon recom- 

 mendation of some chemical friends, 

 it was designated gallo-tartaric acid. 



Pyrogallic acid, a substance at the 

 present time well-known to photo- 

 graphers and photo-micrographers, 

 next claims our attention, and will 

 yield at least two good forms to the 

 student of crystallography. By mak- 

 ing a cold saturated solution of this 

 acid in water and placing a drop upon 

 the slide, it will very quickly cover the 

 spot with long needle-shaped crystals ; 

 but if a very minute shower of some 

 insoluble foreign substance be allowed 

 to fall upon the solution when on the 

 slide, the effect is grand, — each 

 minute speck forming a nucleus 

 around which the needle-shaped crys- 

 tals gather, forming, if examined 

 with a selenite slide, so resplendent 

 an object that no words of mine can 

 adequately describe it. 



Hippuric acid will also be found 

 worthy of all the attention that can be 

 given to it, and upon experiment 

 would probably yield many varied re- 

 sults. I will mention two I have pro- 

 duced, known respectively as circular 

 and floral crystals. 



Circular, or as they are frequently 

 called, wheel crystals, may be obtained 

 by making a strong solution in pure 

 alcohol ; in this case methylated spirit 

 not answering sufficiently well. Drop 

 on a warm slide a little of this solu- 



