I/O 



THE AMERICAN MONTHLY 



[September, 



all cases where a very volatile solvent 

 is used, the results are not so good as 

 when a slower process of crystalliza- 

 tion can be employed. 



In the case of salicine and santo- 

 nine a solution does not give so good 

 a result as the process of fusion, and 

 this process may be adopted in at 

 least two different ways : by fusion 

 only on the surface of the slip and 

 fusion between the slip and cover 

 glass. The best results I have ob- 

 tained by placing a small portion of 

 either salt on the centre of a slide 

 and heating until fusion takes place ; 

 and here I may warn you that a greater 

 heat is required than in any other 

 crystals mentioned, and although in 

 other cases the slip may be held be- 

 tween the fingers, I would recommend 

 that now a clip be used. One of those 

 known as American clothes pegs 

 answer admirably. When fusion has 

 taken place, it is necessary to spread 

 the fused mass with a hot needle over 

 the desired surface, keeping the slide 

 still heated until this is done. As the 

 slide cools the crystals will be formed. 

 I have been informed that for these 

 slides castor oil is the best mounting 

 medium, but have invariably mounted 

 them in pure Canada balsam, and I 

 think with good effect. 



This process of fusion will be found 

 to be of great advantage in many 

 other cases ; but fusion of the second 

 kind mentioned may also, in the case 

 of santonine, be chosen with good 

 results, as the process of fusion under 

 the cover-glass, renders the film of 

 extreme tenuity, and in this case pro- 

 duces a slide of wavy crystals, extreme- 

 ly beautiful under a spot lens, and also 

 very permanent. 



Of another mode of producing in- 

 teresting micro-crystallizations, that of 

 sublimation, I can only indicate broad- 

 ly the methods to be employed, as I 

 have not experimented much in this 

 direction ; but it is a process which 

 must not be passed over, yielding, as 

 it does, good results in the case of 

 benzoic acid, anthracene, anlhraquin- 



one, iodine, naphthaline, and many 

 others. 



To obtain results by this process, it 

 is really only necessary to place a 

 little of the material in a small box, — 

 a match box for instance, and cutting 

 a hole in the lid of the size required, 

 placing a slide, with its well cleaned 

 surface downward over the hoie. If 

 this is placed in a warm place, the ma- 

 terial will sublime and condense again 

 on the glass above. Of course, should 

 great heat be required, in the process, 

 it will be necessary to use something 

 better than the box described ; ahd 

 the material to be sublimed may be 

 placed in a test tube, and the test tube 

 being held by a clamp at the proper 

 distance above a spirit lamp, the slide 

 may rest with its central portion over 

 the mouth of the tube, and will thus 

 receive the sublimation. 



Of the crystallization of fatty acids, 

 which would of itself afford ample 

 occupation for any one wanting a sub- 

 ject, I can say nothing now. 



And of the combination of two or 

 more salts, which is a subject requir- 

 ing, and which will reward, any amount 

 of investigation, I can only outline the 

 matter by saying that fine slides have 

 been produced of various salts of cop- 

 per and magnesia, copper and ammo- 

 nium, copper and potassium, chromium 

 and potassa, chromium and ammonium 

 and many others, and of which proc- 

 ess of combination the platinocya- 

 ninde are fine illustrations. 



Some crystals possess a power 

 known as dichroism, or the presenta- 

 tion to the observer of two colors, ac- 

 cording to the direction of the light, 

 and which is said to depend upon the 

 absorption of some of the rays of light 

 in the passage through the crystal. 

 This power is possessed by acetate of 

 copper, chloride of paladium, and by 

 the oxalate of chromium and potash 

 and others. Other crystals possess a 

 character which by some is termed 

 dichroism, but which is, I think, most 

 properly designated fluorescence, and 

 and is well shown in the platino- 



