114 



CONTRIBUTIONS TO THE KNOWLEDGE 



There is little doubt that all descriptions of coal gas expe- 

 rience some loss of illuminating principles on exposure to a 

 cold of 32°, but the gases richest in hydrocarbons will lose 

 generally the largest proportion ; and hence the advantage of 

 diluting such gases so as to afford more space for the vapours 

 of these hydrocarbons, and thus prevent their condensation. 

 This advantage is seen most strikingly in the behaviour of 

 Boghead gas, with and without water gas, when exposed to 

 the ice test. The difference in the case of Lesmahago would 

 probably be still more striking, as, from the much greater 

 density of its hydrocarbons, it might be expected to lose a 

 large proportion when submitted to the ice test in its pure 

 state. 



For the purpose of comparison with the above experi- 

 ments, I have analysed the gases supplied to consumers from 

 the Manchester Corporation works, and by several of the 

 London companies. The specimens were all collected by 

 myself ; that of the Manchester gas in June, and those of the 

 London gases on the 15th of July, 1851. In some instances 

 they were taken from the burner of the consumer, in others 

 at the works. At the offices of two of the London com- 

 panies I was kindly permitted to take the illuminating power 

 of the gas by means of a Bunsen's photometer ; the illumi- 

 nating power of the other gases is deduced from the analytical 

 results. 



I have assumed that the sperm candles used in the experi- 

 ments just alluded to were burning 130 grs. of sperm per 

 hour, and have corrected the observations to the standard of 

 120 grs. per hour. For obvious reasons, I omit the names of 

 the companies by whom the various gases were supplied. 



The following are the numbers obtained : — 



