250 Scientific Intelligence. 



It follows that after 40 hours drying at 100° the oxide has 

 reached a constant weight and still retained - 59 per cent of 

 moisture. When heated to 160-165° till constant in weight it 

 had lost 0*22 per cent of oxygen. 



It was next attempted by a shorter second heating and a 

 lower temperature to expel the water alone. Silver oxide was 

 dried for 20 hours at 100° and was then heated for 2 hours to 

 130°-135° C. Of this oxide 1-8043 gram was ignited and 

 left 16701 grain of silver, indicating a loss by ignition of 

 7 '44 per cent. This was only -07 less than when the heat was 

 not raised above 100° C, showing that the oxide is not dehy- 

 drated by exposure to a temperature of 130°-135° C. 



The conclusion to be drawn would apparently be that the 

 point at which the last portions of water were driven off was 

 very close to that at which oxygen began to be disengaged. 

 It can be shown however that this is not so and that oxygen is 

 lost long before the last portions of water escape. This can be 

 proved by the delicate photochloride reaction which I de- 

 scribed some years ago. If the silver oxide, dried as above 

 described at 100° C till it reaches a constant weight, is 

 moistened with dilute hydrochloric acid, a chloride is obtained 

 of a deep lilac color. This color always denotes the presence 

 of hemichloride due to the fact that a certain portion of the 

 oxide had been reduced to hemioxide. The hemichloride 

 combining with the white chloride forms a photochloride char- 

 acterized by the coloration just mentioned. 



A really accurate estimation of silver oxide is therefore im- 

 possible, as it loses oxygen too easily. 



Silver oxide is not supposed to form a hydrate, nevertheless 

 some portion of moisture remains united with it more strongly 

 than some part of the oxygen with which it combines to form 

 a strong base. 



But it also appears that the loss of oxygen is very small and 

 soon ceases even at 160°- 165° C. For after 5 hours exposure 

 to that temperature, the weight became constant. 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. On the Phenomena of Coal-dust Explosions. — Thorpe has 

 described a lecture experiment to illustrate the phenomena which 

 are observed in explosions wherein light combustible solids like 

 coal dust suspended in the air are the chief combustibles. In coal 

 mines opinions are divided as to whether coal dust alone in the 

 air can give rise to explosions, or whether it can do so only when 



