160 Scientific Intelligence. [Aug. 



a hardened steel plate to soft steel, or copper, w said to have 

 placed beyond a doubt the most important fact that water sub- 

 mitted to a pressure of 326 atmospheres is diminished in bulk 

 about -^th, or 3^ per cent. 



V. Pure Potash. By Dr. Prout. 



Many practical chemists are doubtless aware of a fact which 

 ouo-ht to be known generally ; viz. that what is usually consi- 

 dered as pure potash almost always contains a minute quantity of 

 some metal. This may be rendered sensible bypassing a current of 

 sulphuretted hydrogen through a solution of such potash, the solu- 

 tion instantly assuming more or less of a dark colour. Some years 

 ago I made a great number of experiments on this subject, and I 

 never was able to procure a specimen of potash or soda which did 

 not become coloured when treated as above. The metal (or rather 

 oxide) present is probably, in most instances, silver (derived from 

 the silver vessels in which it is prepared), but sometimes it appears 

 to be lead, and sometimes iron, or copper. One or other of 

 the latter is very likely to be present if the common subcarbo- 

 nate of potash of commerce has been employed, which is 

 frequently so very impure that I have seen it become quite black 

 upon simple exposure to the fumes of sulphuretted hydrogen. 

 The presence of these metals in the alkalies has doubtless often 

 misled chemists by inducing unnatural appearances. I may 

 mention one striking instance. Some years ago, Mr. Miers 

 announced that he had discovered a gas having the property of 

 precipitating potash and soda black.* This gas was a mixture 

 containing sulphuretted hydrogen, and the precipitates arose 

 from metaUic impregnation in the alkaline solutions employed. 



VI. Urine of the Horse. By the Same. 



As the urine of the horse has been said to contain very little 

 urea, 1 was induced lately to examine it with the view of deter- 

 mining that point. The rfcsult was, that it contained an unusually 

 large proportion of that principle, so that, without being pre- 

 viously concentrated by evaporation, it yielded crystals of 

 nitrate of urea very readily on the addition of nitric acid. This 

 fact accounts, therefore, for the strong ammoniacal odour of 

 stables. The urine which was subjected to the above experi- 

 ment was nearly transparent, and of a pale amber colour. It 

 was rather of a mucilaginous consistence, foamed a good deal 

 on shaking, and passed through the filter with great difficulty. 

 It was not sensibly acid or alkaline, and its specific gravity was 

 1029-3. 



Those who wish to repeat this experiment should operate upon 

 the urine while still warm, or, if this is not convenient, should 

 put a few drops of some acid (the muriatic is preferable) into the 

 vessel in which it is voided and intended to be kept. This, by 



• See Jnnals of Philosophy, vol, iv. p. 191. 



