348 Dr. Hcrapath on the Manufacture of Crystals of 



tions would result ; therefore the flask or matrass answers better 

 than the evaporating dish. 



4th. It is also decidedly an advantage to have a broad surface 

 in proportion to the depth of liquid ; the reason being, that the 

 thinner and most easily reached plates form on the surface and 

 float there until the time arrives to remove them ; and the greater 

 the surface, the more numerous are the plates. 



5th. These broad plates are not always formed ; but if after 

 six hours none make their appearance, it is merely necessary to 

 apply a spirit-lamp to the bottom of the flask and warm the 

 liquid to dissolve all the deposited crystals, then add a little spirit 

 and a few more drops of iodine solution and again wait for cry- 

 stallization. 



6th. Supposing that we obtain a crop of these broad floating 

 plates, which generally occurs under the aforementioned con- 

 ditions, we permit them to remain from twelve to twenty-four 

 hours to complete their disc and fill up all crevices, &c, and to 

 attain a sufficient degree of thickness ; for if too thin, they do 

 not stop the red or purple-violet rays, as Haidinger has beauti- 

 fully shown and admirably explained (wife Phil. Mag. Oct. 1853, 

 and PoggendorfPs Annalen for June last). If the crystals are 

 allowed to remain too long in their mother-liquid, we run the 

 risk of loss and injury ; for after some time a dissolving or dis- 

 integrating action appears to occur, and considerable disappoint- 

 ment is occasioned.- I have lost several batches of beautiful and 

 magnificent plates from inability to secure them at the nick of 

 time. 



Having by these means obtained the object of our best wishes, 

 it now remains to secure the prize. This requires a little patience 

 and a tolerable amount of care ; the following plan is the most 

 ready, and requires but little practice and a steady hand to ensure 

 success. 



The first stage of the process is to procure a table as near as 

 possible to the crystallizing spot, furnished with the following 

 apparatus : — 



1. A gallipot or small mortar to hold the flask on as a support. 



2. A supply of perfectly clean circular glass discs, small 

 enough to pass down the neck of the flask with ease. 



3. A glass rod of sufficient length to descend to the bottom 

 of the flask if necessary. 



4. A little marine glue or sealing-wax. 



5. A spirit-lamp and matches. 



6. A quantity of blotting-paper cut in strips about an inch 

 wide and two inches long, and also a folded sheet of the same to 

 act as a pad or support. 



Now remove the flask with the greatest amount of care from 



