1819.] Scientific Intelligence: 469 



presence of an alkali. The water being evaporated to dryness 

 left a white crust on the glass, which was tasteless, insoluble in 

 water, but soluble with effervescence in nitric acid, and the solu- 

 tion was precipitated white by oxalate of ammonia. It was, 

 therefore, carbonate of lime ; so that the alkaline properties of 

 the water were derived from some lime which it held in solution.- 



The residual matter dissolved without effervescence in muria- 

 tic acid, and was precipitated white by ammonia. It was,' 

 therefore, phosphate of lime. 



Thus the calculus was composed of 



Uric acid, 

 Phosphate of lime, 

 Lime. 



I think it not unlikely that the lime had been in combination 

 with the uric acid ; but the quantity of calculus (amounting only 

 to three or four grains) was too small to enable me to determine 

 the point by a more rigid analysis. 



The fact, however, of pure lime being separable by muriatic 

 acid, and by water after simple exposure to a red heat, I think 

 of some importance. I am not aware that it has been hitherto 

 observed. 



III. Query respecting the Method of coating Metals xoith 

 Platinum. By T. Howse, Sen. 



(To Dr. Thom30D.) 

 SIR, Cirencester, Sept. 21, 1819. • 



From some directions for washing metals by means of amal- 

 gams, in Rees's Cyclopaedia, I was led to hope that it would be 

 a matter of no great difficulty to apply the valuable metal plati- 

 num to some of the common purposes of life. According to 

 those directions, I have precipitated platinum from its solution 

 by adding muriate of ammonia, heated the precipitate to expel 

 the acid and oxygen, and afterward heated it again with the 

 addition of mercury, to form an amalgam, for the purpose of 

 coating brass or copper, from which the mercury was to be driven 

 off by heat applied to the article coated with the amalgam. I 

 have tried several variations of the process, but hitherto without 

 success ; 1 should, therefore, feel obliged if you would furnish 

 me with the method actually practised, if it be known, through 

 the medium of your Annals. I fear that a covering of platinum 

 laid on by means of mercury, must, if practicable, be so thin as, 

 to possess little durability. A chemical friend informs me that 

 copper articles plated with platinum, the two,metals being in the 

 proportion of 15 to 1, may be purchased of M. Laboute, rue 

 Neuve-Saint-Eustache, No. 4, at Paris, at about 37s. per pound ; 

 but he is not aware that this method of plating is yet published, 

 I remain, Sir, your constant reader, 



T. Howse, 



