156 



THE AMERICAN MONTHLY 



[August, 



short and flattened four-sided prisms 

 which show well by polarized light, 

 and possess the analytic character re- 

 ferred to later. 



Besides the sails of ammonia de- 

 scribed, may be enumerated the borate, 

 muriate, phosphate, sulphate, urate, 

 and platino-cyanide ; with these I have 

 had but little experience. I may say, 

 however, that of themselves, and in 

 combination with other things, you 

 will find them worthy objects of study 

 or amusement. 



Turning now to magnesium, we find 

 that at present there are not so large 

 a number of its salts that are recog- 

 nized as micro-crystals ; but I must 

 not omit from these the well-known 

 Epsom salts, or magnesium sulphate, 

 which will produce, according to the 

 mode of crystallization, very var3dng 

 results. The most typical and one 

 readily produced, is obtained from a 

 saturated, or nearly saturated, aqueous 

 solution, which, if allowed to crystallize 

 very slowly on a slide, will result in 

 much larger crystals than if the slide, 

 with a drop of the solution, is very 

 gently warmed. These crystals, if 

 mounted in pure balsam, will, with 

 selenite, form a brilliant slide. 



Ammonio phosphate of magnesia, 

 or as it is frequently called, triple 

 phosphate, is like the murexide re- 

 ferred to before, a production from 

 urine, and occurs in many different 

 forms, of which the one known as the 

 prismatic form is the most frequent. 

 This salt is not a'commercial product, 

 but it is said that the crystals may be 

 obtained by allowing urine to decom- 

 pose, or by diluting the secretion with 

 water and adding in small quantities 

 dilute ammonia solution. 



One other salt of magnesia, the 

 platino-cyanide, must be referred to, 

 and as well as being one of the most 

 beautiful, it is, of the platino-cyanides 

 the most easy to prepare. Most of 

 them, it will be found upon experi- 

 ment, offer almost insuperable ob- 

 stacles to any but a scientific chemist. 

 To obtain these micro-crystilliza- 

 tions, make a strong, but not quite 



saturated solution in pure alcohol, and 

 place a drop on a cold slide, which 

 should be covered with a shade of 

 some kind to prevent the too rapid 

 evaporation of the alcohol. A watch 

 glass will answer this purpose, which 

 allows time for the gradual building 

 up of the desired crystal, but if, as 

 frequently happens, it is found that 

 good crystals have not been produced, 

 drop upon the same spot a little more 

 of the solution : this will re-dissolve 

 the crystals already formed. Again 

 cover with a shade, and in due time 

 new and probably better crystals will 

 be formed. When the crystallization 

 is satisfactory and is also thoroughly 

 dry, the slide may be mounted in bal- 

 sam and benzole. 



( To b; Continued. ) 



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Mounting Algm. — G. Berthold 

 has been experimenting with different 

 media in the hope of finding some- 

 thing which would preserve marine 

 algai with the least possible disturb- 

 ance of the structure of the proto- 

 plasm. Picric acid, osmic acid, and 

 iodine dissolved in fresh water were 

 tried without satisfactory results owing 



