154 



THE AMERICAN MONTHLY 



[August, 



tion and immediately hold over a spirit 

 lamp, removing the slide from warmth 

 directly the crystals begin to form ; 

 but should the crystallization stop, it 

 can be caused to recommence by again 

 warming. 



Floral crystals may be obtained 

 from the same solution, but it must be 

 dropped upon a cold slide ; and if the 

 slide is gently waved about to evapor- 

 ate the alcohol, the floral crystals will 

 form ; and the suggestion may be 

 offered, though I have never put it to 

 experiment, that if a rotary movement 

 is given to the slide, the crystals, as 

 they form, will be a combination, pos- 

 sibly taking the character of circular 

 florets. 



As a conclusion to my selection 

 of acid crystallizations, your attention 

 must be directed for a moment to 

 citric acid, which, although a most 

 difficult form to produce, is so strik- 

 ingly beautiful that it deserves the 

 expenditure of all necessary time and 

 trouble. The most successful plan 

 with this acid is. to make a very strong 

 solution in cold water, place a drop on 

 the centre of slide, and at once pour 

 ofif all surplus fluid, leaving as it were 

 only a film. Put the slide on one side 

 for a short time, say half an hour, then 

 warm very gently and but slightly, and 

 allow to cool very gradually ; repeat 

 these operations until the rosette crys- 

 tals are formed. This may occur at 

 the first cooling, or it may take several 

 applications; sometimes, in fact, it is 

 found impossible to cause them to 

 form at all, and as it is noticable that 

 when formed, too much heat will 

 cause them to disappear, it may be 

 that too great a warmth in one of the 

 warmings is the cause of their non- 

 appearance. 



All the crystals yet described, ex- 

 cept the last, should be mounted in 

 pure Canada balsam; but this last pre- 

 paration is best mounted in a solution 

 of evaporated balsam in benzole. 



Passing now from the acids to the 

 salts of some of the metals, I would 

 direct your attention to potassium and 

 sodium, which yield with little trouble 



many good forms of micro-crystalliza- 

 tion. These salts include the arseniate, 

 carbonate, chromate, and bichromate, 

 bitartrate,' chlorate, iodide, nitrate, 

 oxalate, ferricyanide, ferrocyanide, sul- 

 phate, urate, etc. Of these I need 

 only mention one or two which have 

 been brought more particularly under 

 my own observation and preparation. 



As in the acids, I will refer first to 

 one that offers but little difficulty to 

 the amateur mounter — the chlorate 

 of potash. The most typical form of 

 this salt is that in which the crystals 

 are each separate and distinct. To 

 obtain these it is necessary to make a 

 strong solution in hot water, and to 

 place a little of this solution upon a 

 slide (previously breathing upon the 

 slide, which causes the liquor to spread 

 evenly). The slide must then be 

 placed on one side, that the crystalliza- 

 tion may proceed gradually, and if the 

 solution has been made from pure 

 chlorate, the crystals will be large and 

 fine. 



For the imperfect, or as they are 

 generally known, the dendritic crys- 

 tals, place a little of the same solution 

 upon a slip and heat over a spirit 

 lamp. Immediately the crystals begin 

 to form ct any point, at once tilt the 

 slide away from that point, so that 

 all surplus liquor may run off, then 

 continue the crystallization by gentle 

 warmth. 



Somewhat similar in outward ap- 

 pearance to separate crystals of potas- 

 sium chlorate, I may here mention 

 those of sodium nitrate, which are 

 however, obtained in a slightly differ- 

 ent manner, and offer a little more 

 difficulty in the production. 



A strong, nearly saturated solution, 

 must be prepared in cold water, and a 

 drop put upon a cold slide. In a very 

 short time crystals will reveal them- 

 selves as small points rising from the 

 surface of the liquor. At once all sur- 

 plus mother liquor must be poured 

 away, and the slide must be gently 

 warmed over a spirit-lamp ; and at the 

 same moment it will frequently be 

 found advantageous to blow upon the 



