230 Intel! i ire f ice and Miscellaneous Articles. 



and in every instance procured ammonia from them, even after the 

 precaution of washing the finely-powdered ore with boiling water. 

 150 parts of haematites iron ore from Spain yielded 2 parts of mu- 

 riate of ammonia. — Annates de Chimie et de Physique. 



DETECTION OF HYDROCYANIC ACID. 



MM. Lassaigne and Leuret have made several experiments upon 

 the use of persulphate of iron and of copper, in detecting the pre- 

 sence of hydrocyanic acid in the contents of the stomachs of animals 

 which have been killed by a dose of from two to five or six drops of the 

 pure acid. They found that hydrocyanic acid cannot be discovered 

 in animals which have been killed by small doses of it, if the bodies 

 are previously exposed to the air for two or three days; that after a 

 longer time tlian this, the disappearance of the poison is due to its 

 decomposition, which is favoured by the presence of putrescent animal 

 matter : and they state that when it is requisite to examine a body to 

 ascertain the presence of this poison, it should be done as soon as 

 possible after death Journal de Chem. Med. 



TRANSFERENCE OF HEAT BY CHANGE OF CAPACITY IN GAS. 



Many of tlie copper vessels in vvliich gas is compressed at tlie 

 Portable Gas-works are cylinders, from two to three feet in length, 

 terminated by hemispherical ends. These are attached at one end 

 to the s}'stem of pipes by which the gas is tlirown in, and being so 

 fixed the communication is opened: it fre(]uent!y happens that gas, 

 previously at the pressure of thirty atmospheres in the pipes and 

 attached recipients, is suddenly allowed to enter these long gas 

 vessels, at which time a curious effect is observed. That end of the 

 cylinder at which tlie gas enters, becomes very mucli cooled, 

 whilst, on the contrary, the other end acquires a considerable rise 

 of temperature. This effect is produced by change of capacity in 

 the gas : for as it enters the vessel from the parts in which it was 

 previously confined, at a pressure of thirty atmospheres, it sud- 

 denly expands, as its capacity for heat increases, falls in tempera- 

 ture, and consequently cools that part of the vessel with which it 

 first comes in contact; but the part which has thus taken heat, from 

 the vessel being thrust forward to the further extremity of the cy- 

 linder b}' the successive portions which enter, is there compressed 

 by them, has its capacity diminished, and now gives out that heat, 

 or a part of it, which it had the moment before absorbed : this it 

 comnmnicates to the metal of that part of the gas vessel in which it 

 is so compressed, and raises its temperature. Thus the heat of tem- 

 perature is actually taken up by the gas from one end of the cylin- 

 der and conveyed to tiie other, occasioning the difference of tem- 

 perature observed. The effect is best observed when, as before 

 stated, the gas at a pressure of thirty atmospheres is suddenly let into 

 the vessels ; the capacity for the parts is such, that the pressure 

 usually sinks to about ten atmospheres. — Royal Institution Journal, 

 N.S. July. 



ANALYSrS 



