Intelligence and Miscellaneous Articles. 3D5 



bottom of a smrill glass tube, after having rolled it up, tluit it may 

 occupy less space. When healed the mercury is volatilized and 

 condenses in the upper part of the tube, the end of which has been 

 previously drawn out by the lamp. No such effect is produced if the 

 whitening has been occasioned by tin. 



M. Orlila concludes, from the above and some other experiments, 

 that the small apparatus invented by Mr. Smithson cannot be de- 

 Ijended ujjon for the detection of small quantities of mercury, unless 

 metallic mercury be separated from the gold by distillation, as above 

 mentioned ; because solutions which contain no mercury, but merely 

 a little acid or common salt, produce appearances similar to those 

 effected by mercury. M. Orlila nevertheless admits that the appa- 

 ratus may be advantageously used, and will detect very minute quan- 

 tities of mercury, by iirst treating the whitened gold with muriatic 

 acid and then subjecting it to distillation. 



ON PHOSPHORIC ACID. BY M. GAY-LUSSAC. 



INL Englchart has observed that phosphoric acid recently fused and 

 dissolved in water precipitates albumen ; a property which it did not 

 previou.sly possess, and which it loses after having been kept for some 

 time in solution. Lately Mr. Clark has discovered that phosphate of 

 soda e.xposed to a red heat, acquired new properties. It becomes 

 less soluble, contains less water of crystallization, changes in form, 

 and precipitates nitrate of silver v,liite, whilst before calcination it 

 precipitates it yellow-. 



These two observations by M. Engleliart and Mr. Clark appear 

 to possess some analogy ; 1 have made some experiments to verify 

 my suspicions. 



1 took some liquid phosphoric acid which had been during a long 

 time in my laboratory, and having ascertained that it did not preci- 

 pitate albumen, I saturated a part of it with carbonate of soda ; the 

 phosphate which I obtained precipitated nitrate of ailver of a yellow 

 colour. 



Another portion of the same acid, calcined, and then saturated 

 with soda, ])recipitated nitrate of silver white. Lastly, calcined phos- 

 phate of soda was decomposed by acetate of lead, and the phospliale 

 of lead obtained was decomposed by sulphuretted hydrogen. The 

 I)hosphoric acid separated precipitated albumen, and combined with 

 soda it precipitated nitrate of silver white. 



It results from these observations, that the remarkable change of 

 properties, observed by Mr. Clark in the calcined phosphate of soda, 

 is derived from the same cause which jjroduces the same cflect with 

 phosphoric acid in similar circumstances. What proves it still further 

 is, that phosphate of soda and phosphate of ammonia, made with 

 calcined i)hosphoric acid, precipitate nitrate of silver white, and that 

 common phosi)hate of potash acquires the same property by calcina- 

 tion. It is remarkable that the modification which phosphoric acid 

 undergoes by heat is much more ])ermanent when it is combined 

 with a l)a."ic, than wlicn simply dissolved in water. Mr. Clark's opi- 

 nion of the cause of these ph.unoniena appears to require some modi- 

 fication. 



'.) K '-' LIST 



