SQ* Intelligefice and Miscellaneous Articles. 



such a proportion that the quantity added should equal three-fourths 

 the bulk of the acid. When the mixture has become cool, drop in a 

 concentrated solution of protosulphate of iron, which if any nitric 

 acid is present decomposes it, causing the evolution of nitric oxide 

 which produces the rose-red or purple tint above alluded to. This 

 mode of operating will allow us to detect 1 part of nitric acid in 

 24,000 of water. 



For the detection of nitrogen gas, De Richemont directs the gas 

 under examination to be mixed with from 3 to 6 times its volume of 

 a mixture of oxygen and hydrogen (in equal vols.) and the whole 

 detonated in a Eudiometer by the electric spark. The fluid that 

 bedews the Eudiometer after the explosion is to be mixed with sul- 

 phuric acid, to which a few drops of protosulphate of iron in solu- 

 tion have been added : the fluid will assume the rose-red tint if the 

 minutest portion of nitrogen is present. It is of course necessary to 

 avoid any source of fallacy arising from the presence of atmospheric 

 air in the oxygen and hydrogen employed. The action of sulphuric 

 acid in producing this rose colour is so remarkable that when we have 

 failed in detecting the presence of nitric acid by the ordinary process 

 from its being present in too small a quantity to tinge the sulphate 

 of iron brown, the addition of concentrated sulphuric acid will deter- 

 mine the production of the rose-red tint, if any nitric acid existed 

 in the fluid under examination. — Journ.fur Pract. Chemie, 5. 207. 



FORMATE OF SODA, AS A REDUCING SUBSTANCE FOR METALLIC 



POISONS (arsenic). 

 Gobel has found that formate of soda furnishes the most ready 

 means of reducing metallic poisons, not only when in the state of 

 oxides but as sulphurets, and is therefore of extreme importance in 

 researches connected with medico-legal inquiry. The substance to be 

 examined is mixed with the formate and heated in the usual manner 

 in a small glass tube, over the flame of a lamp ; the arsenic if present 

 of course sublimes : in this way Gobel has detected the presence of 

 orpiment in the golden sulphuret of antimony when present only in 

 the proportion of 1 part to 1000 of the antimonial sulphui'et. — Jahres- 

 Bericht der Phys. Wissenschaften, 16. 162. 



ON THE TRANSPARENCY OF CARBON. BY DEGEN. 



Degen has attempted to prove that charcoal in very thin layers 

 possesses a very considerable degree of transparency, and appears of a 

 yellowish-brown colour. To demonstrate this he placed a piece of 

 pine charcoal on burning coals in a small furnace, so close that very 

 little air could enter it, so that the piece of charcoal should undergo 

 combustion in an atmosphere loaded with carbonic acid : under these 

 circumstances the more porous portion burns, whilst the denser 

 portion, consisting of an aggregation of small vessels, is left : the walls 

 of these carefully examined under a microscope, appear translucent. 



If a piece of glass covered with lac-varnish and sprinkled with 

 charcoal powder is ignited in a crucible, so as to carbonise the 

 varnish, the thin layer (oi carbon }) left is transparent and yellowish 

 brown. — Poggendorff's Annalen, 35. 468. 



