The Microscope. 167 



upwards, the usual laboratory process is to put it into a watch- 

 crystal or small evaporating- dish and hold it ovor the flame of the 

 lamp or on the bath, applying the heat carefully. As the crystals 

 begin to form, a pointed glass rod is drawn over the surface of the 

 container, making little furrows around which the crystals form. 



When the liquid is in lesser quantities, — only a drop, or maybe 

 two or three minims, it is put upon a slide or watch crystal that has 

 previously been heated, and the pointed rod used as before. Should 

 the heat not be sufficient, a second slide is made quite hot and shoved 

 under the first, the process being repeated as often as necessary. 



The crystals thus obtained are rarely satisfactory, and very 

 frequently it is possible to obtain nothing moi'e than an amorphous 

 powder, when we know crystallizable matter exists and should be 

 recovered. 



Some years ago, while making some experiments requiring the 

 crystallization of very small quantities of fluids, the following plan 

 was suggested to me — whether by something I had read or seen, or 

 whether it came intuitively, I do not now remember, it is so long ago : 



Provide two watch-glasses of nearly the same size and shape so 

 that they fit snugly into each other. Into one of these pour the liquid 

 to be crystallized, and having warmed the other by passing it 

 through the flame of the lamp, or dipping it into hot water, place it 

 immediately on top of the globule of fluid, letting it settle to place 

 of its own weight. The fluid is thus spread out into a tenuous film 

 between the two watch-glasses. 



Now place the glasses upon a piece of felt, two or three thick- 

 nesses of blotting-paper, or some other non-conducting material, and 

 with a pipette pour into the cavity of the upper crystal a half fluid 

 drachm of rhigoline, benzol or ether, and blow on it with the lips. 

 In a moment the rapid volatilization of the liquid will produce a 

 great lowering of the temperature, and the film of liquid between 

 the glasses will commence to deposit its crystals. Sometimes this 

 occurs instantaneously, but generally it requires from 15 seconds to 

 a minute to thoroughly cool the glasses. The application of volatile 

 fluid must be repeated if necessary. 



As soon as the deposition of crystals ceases take a bit of blot- 

 ting, or filter-paper and pass the edge of it between the watch- 

 glasses and absorb the remaining mother liquor, leaving the ciystals 

 nearly dry. The upper glass may now be removed, and the lower 

 one, with its crop of crystals, placed directly on the stage of the 

 microscope, or, if necessary, the crystals may be collected and 

 washed before examination. 



