t5*2 Scientific Intelligence. [Aug. 



The effect of the heated air has commonly l)een attributed to the 

 absence of the cooling power, which was exercised by the cold air 

 on its being introduced in contact with the heated contents of the 

 furnace. Berthier denies that this is the mode in which it operates. 

 He thinks that the phenomena which result from the employment of 

 hot air proceed from the greater activity of the combustion in the fur- 

 nace, than when the air has not been previously heated, that is to say, 

 that with the same weight of air there is more oxygen absorbed in 

 the first case than in the second. If this opinion is correct, it follows, 

 that less hot air will be required than of cold air for the combustion 

 of an equal quantity of charcoal in the furnace, and that the air 

 which proceeds from the latter being possessed of little oxygen, can- 

 not support combustion. Now, the exhaustion of the oxygen in the 

 air is a point of essential importance, when we wish to obtain a very 

 strong heat, for the azote of the air only assists in producing a loss 

 of the portion of the heat developed by combustion. Hence, the 

 less air that is consumed the less does this cause of cooling operate. 

 Besides, the affinity of gas for solid substances is increased by the 

 heating of the gas. 



It has been said that effects similar to those produced by heated 

 air, may be obtained by the employment of cold air sufficiently com- 

 pressed, or what would be extremely powerful, the use of hot air 

 compressed to such a degree as experience might point out. 



III. — Action of Muriate of Ammonia upon some Sulphates, 

 and upon Silver. 



M. VoGEL has found that the sulphates of iron, copper, and man- 

 ganese, are partly decomposed by a solution of sal-ammoniac. This 

 action produces two double salts, the one which crystallizes first is 

 the sulphate of ammonia and metal, the other more soluble is the 

 muriate of ammonia and metal. 



2. Sulphate of lime is more soluble in water charged with muriate 

 of ammonia than in pure water, but it is not decomposed by this 

 salt, and the sulphate of barytes is not soluble in a solution of this 

 salt. 



3. Sulphate of lead is completely decomposed by a solution of 

 sal-ammoniac, from which result muriate of lead and sulphate of 

 ammonia. 



4. A solution of sal-ammoniac acts upon silver with the assistance 

 of the air and dissolves it. 



5. A concentrated solution of sal-ammoniac may dissolve a notable 

 quantity of chloride of silver, of which the greater part is precipitated 

 by water. 



6. Chloride of silver is still more soluble in a boiling solution of 

 sal-ammoniac. 



7- The vapour of sal-ammoniac carried over pure silver heated 

 to the temperature at which glass softens, disengages ammoniacal 

 gas. — (Jonrn. de Pharm. xx. 514.^ 



