440 Crystals for the Micro -Tolariscope. 



The whole process will be found to occupy scarcely more 

 time than it has taken me to describe it, and a dozen slides 

 may be prepared with as little trouble as is required for a 

 single one by the usual method, and with far greater certainty. 

 It may be objected that, as in this way of operating, quantities 

 of the salts are required which are much greater than are 

 necessary where merely a few drops of a solution are crystal- 

 lized upon the slide, it could not well be carried out in the case 

 of rare or expensive substances. This, however, is not the 

 case. 



Where but a small quantity of the salt is obtainable, 

 results equally good may be had by crystallizing upon the 

 cover glass instead of upon the slide. The cover glasses, which 

 for this purpose should be circular and pretty thick, are cleaned 

 in just the same way as has been described for the slides, and 

 being held by their edges with the forceps are immersed in the 

 hot solution. This modification of the method of operating 

 will, of course, necessitate a corresponding alteration in the 

 process of mounting, which I shall afterwards describe. 



Where access can be obtained to a large number of crys- 

 talline substances, it is an interesting as well as instructive 

 amusement to ascertain by experiment which of them form 

 good polariscope objects. The following list will, however, be 

 found to include most of the salts worth mounting. In the 

 case of substances which require some departure from the 

 general mode of manipulating which I have recommended, I 

 shall describe that modification of it which is most adapted to 

 each particular crystalline body. 



Acid, citric. Lime, tartrate. 



„ tartaric. Magnesia, sulphate. 

 „ uric. „ platinocyanide. 



Ammonium, chloride. Mercury, bichloride. 



,, oxalate. Napthaline. 



„ oxalurate. Narcotine. 



Antimony, potassio-tartrate. Potash, bicarbonate. 

 Asparagine. „ binoxalate. 



Baryta, nitrate. „ chlorate. 



Cadmium, sulphate. „ nitrate. 



Caffein. Quinine, iodide. 

 Chromium, ammonia oxalate. „ iodo-sulphatv. 



„ potassa oxalate. Salicine. 



Copper, acetate. Santonine. 



„ ammonio chloride. Sugar of milk. 



„ sulphate. Thallium, sulphate. 



„ magnesia sulphate. Vanillin. 



Lead, acetate. Zinc, sulphate. 



