Chemical Science. 185 



9. Preservation of Crystals. — It is sometimes an object to 

 preserve good crystals of salts, especially with those who are 

 attentive to the study of crystallography. In attaining this end 

 much assistance may be derived from the use of sweet oil. 

 Many crystals, which change and become dull by exposure to 

 air, as alum, sulphate of copper, sulphate of iron, prussiate of 

 potash, Sfc. ; if slightly oiled, do not then alter in a long time, 

 and many efflorescent substances are prevented from changing 

 by the same means. Even crystals of Glauber's salt will lie 

 exposed to the air for weeks together without efflorescing, if 

 well oiled. Tlie best method is to soak the crystals in oil for 

 a few hours, and then to wipe them, and put them up in bottles. 



10. Pink Sediments of Urine. — Dr. Prout says, " I lately had 

 an opportunity of examining the most marked specimen of pink 

 sediment I had ever seen. It consisted almost entirely of the 

 lithate of ammonia. Pink sediments in general consist either of 

 this substance, or of the lithate of soda, mixed with more or 

 less of the phosphates. When the lithate of soda and the 

 phosphates prevail, the sediment usually assumes the form of 

 what has been denominated the lateritious sediment. In spe- 

 cimens of this latter description I have several times found 

 nitric acid, and in all cases I have satisfied myself that the red 

 colour of these sediments depends upon some slight mixture of 

 the purpurate of ammonia or soda, according as the sediment 

 itself consists of the lithate of ammonia or soda. Perhaps the 

 formation of the purpuric acid may be explained, by supposing 

 that the nitric and lithic acids are secreted together, and that 

 the purpuric acid, or rather the purpurate of ammonia, is form- 

 ed by the action of the nitric upon the lithic acid. — Thomson's 

 Annals, xv. p. 155. 



1 1 . Test for Olive Oil. — If the pernitrate of mercury, made 

 by dissolving 6 parts of mercury in 7.5 parts of nitric acid, of 

 sp. gr. 1.36., at common temperatures, be mixed with olive oil, 

 in the course of a few hours the mixture, if kept cold, becomes 

 solid, but, if mixed with the oil of grains, it does not solidify. 



