658 REPORT— 1895. 



Silver chromate did not suffer appreciable change till above 300°. Metallic 

 silver was found to be present in the residue as well as silver nitrate. The 

 chromium was all converted into the sesquioxide. Some amount of nitrite of 

 silver was also formed. 



Silver siilphate is only attacked at the highest temperature of the furnace. 



It was found in certain cases — e.g., with lead nitrate — that the intermixture of 

 a decomposable oxide — e.g., PbO„or MnOj — with the salt, caused the latter to be 

 attacked at a temperature below that at which action begins with either the salt 

 or oxide taken separately. 



Experiments have also been in progress on the interaction -of nitric oxide and 

 various gases, but the results are not yet quite complete enough for publication. 



4. On the Respirahility of Air in which a Candle Flame has burnt until it 

 is extinguished. By Frank Clowes, D.Sc. 



At the last meeting of the British Association the author stated the composi- 

 tion of artificial mixtures of nitrogen and carbon dioxide with air, which were 

 just able to extinguish various flames. It was found that the flames of ordinary 

 candles and lamps were extinguished by mixtures which contained on the average 

 about 16'5 per cent, of oxygen and 83"5 per cent, of the extinctive gases. A flame 

 of coal-gas, however, required for its extinction a mixture still poorer in oxygen, 

 and containing 11-3 per cent, of oxygen and 88"7 per cent, of the extinctive gases. 

 These results have since been confirmed by a different method. The method con- 

 sisted in allowing the flames to burn in air enclosed over mercury until they were 

 extinguished ; the remaining extinctive atmosphere was then subjected to analysis, 

 and its composition was found to be practically identical with that previously 

 obtained from the artificial mixtures. An analysis of air expired from the lungs 

 proved that it was also of the same composition as that which extinguished the 

 flame of an ordinary candle or lamp. 



The average percentage composition of expired air and of air which extin- 

 guishes a candle flame is as follows: — oxygen 16'4, nitrogen 80'5, carbon 

 dioxide, o'l. 



Now an atmosphere of this composition is undoubtedly respirable. Physio- 

 logists state that air may be breathed until its oxygen is reduced to 10 per cent. 

 The maximum amount of carbon dioxide which may he present is open to question, 

 but it is undoubtedly considerably higher than 3 per cent. Br. Haldane maintains 

 that the above atmosphere is not only respirable, but would be breathed by a 

 healthy person without inconvenience of anj' kind ; he further .states that no per- 

 manent injury would result from breathing such an atmosphere for some time. 



The conclusion to be drawn from these facts is that an atmosphere must not be 

 considered to be dangerous and irrespirable because the flame of an ordinary candle 

 or oil lamp is extinguished by it. The view is very generally advanced that a man 

 must, on no account, venture into air which extinguishes the flame of a caudle or 

 of a bundle of shavings. It will be seen thut this precaution may deter one from 

 entering an atmosphere which is perfectly safe and respirable, and from doing duty 

 of a humane or necessary character. An atmosphere which extinguishes a coal- 

 gas flame, however, appears to approach closely to the limit of respirahility, as far 

 as the proportion of oxygen which it contains is concerned. Hence the coal-gas 

 flame appears to be a more trustworthy indicator of respirahility than the flame of 

 a caudle or oil-lamp. Undoubtedly the candle and lamp flames should be discarded 

 as tests of respirahility of air. 



5. 2'he Action of Light upon the Soluble Metallic Iodides in presence of 

 Cellulose. By Douglas J. P. Berridge, B.A., Malvern College. 



It was shown by Cook, in 1894, that whilst potassium iodide, purified by 

 ordinary methods, is decomposed by light, the salt is not thus affected if purified 

 by either fusion with charcoal or crystallisation from absolute alcohol. Although 



I 



