CHEMICAL SCIENCE. 235 



of chloride of sulphur, and prevent the dampness from decomposing this 

 compound. These hard compounds of oil are not attacked by any atmos- 

 pheric influences ; I have left them for several years exposed to the external 

 air. 



These compounds are not, like vulcanized India-rubber, flexible when cold, 

 but are brittle when handled carelessly, which is an inconvenience. A still 

 greater one is the decided smell which they retain for a long time. 



I have tried to make them as hard as hardened India-rubber, but in vain. 

 Almost all substances introduced into them are altered by the chloride, and 

 add nothing to the hardness. 



They can, however, easily be colored. It requii-es but a little color mixed 

 with the oil before the introduction of the chloride. Some colors, however, 

 are altered by it. 



These compounds resist very well the mineral acids and alkalies when 

 moderately dilute. These alkalies concentrated saponify them finally. A 

 heat of 250 browns them, a higher temperature melts them with a blackish 

 color. This vulcanized oil may be well used for moulds, as it takes impres- 

 sions very sharply. When rubbed, it always keeps a smooth and polished 

 surface. It has electric properties in a high degree, and might be used for 

 plates for electric machines. 



I have not been able to apply this substance upon stuffs, in consequence 

 of its acid reaction, which destroys them. I have plated wood with it, by 

 first roughening the wood so as to cause it to adhere. It may be applied for 

 floor-cloths, table-covers, imitation marbles, window panes, etc. 



I will remark, in conclusion, that the bromide of sulphur has the same 

 properties as the chloride, and it was, in fact, with the former that I made 

 my first experiments at the College of France, in 1853. 



ON THE VARIABLE ILLUMINATING POWER OF COAL-GAS. 



The following paper, on a subject of general and popular interest, read 

 before the American Association for the Promotion of Science, Baltimore 

 meeting, 18-58, by Prof. W. E. A. Aikin, of Baltimore, is published in Silli- 

 man's Journal, Vol. xxvu., No. 78: 



In common with a large number of citizens of Baltimore, my attention 

 was directed, some short time since, to a somewhat sudden, inexplicable, 

 and enormous increase in the amount of our quarterly bills for gas con- 

 sumed; an increase equal at times to an advance of a hundred per cent, over 

 the corresponding quarter of the preceding year. As it would have been 

 absurd to suppose a simultaneous derangement of all the meters over an 

 extensive district, it was obvious that the difficulty could not lie in any error 

 in the registry of the gas, but in its illuminating power, necessarily requiring 

 the consumption of a greater bulk of gas to produce a given quantity of 

 light. Feeling curious to know how this difference could have occurred, I 

 set myself to work to ascertain, if possible, what causes could be acting to 

 diminish the illuminating power of the gas. 



It has long been known that the quality of the gas produced from the fat 

 coals is very materially influenced by the circumstances of the decomposi- 

 tion. In the elaborate experiments made some years ago, on a most ex- 

 tended scale, by Heel ley, the British engineer, as detailed in his report to a 

 committee of the House of Commons, we find this subject most satisfactorily 

 discussed. Below a cherry-red heat, the product obtained by heating coal 



