CHEMICAL SCIENCE. 247 



By the term "purity " is understood entire freedom from carbonic acid 

 gas, sulphuric acid gas, ammonia, vapors of sulphuretted compounds, and 

 water. 



A pure illuminating gas consists of a mixture containing carburetted 

 hydrogen, carbonic oxide, hydrogen and nitrogen, olefiant gas, and vapors 

 of benzole and naphtha. 



The addition of the gases before named either diminishes the value of 

 an illuminating gas by increasing the volume, or, as in the case of carbonic 

 acid gas, it reduces the illuminating power in the act of combustion. 



Referring to my records, I find the value of Boston gas averaged from 

 daily observations for the year 1853 was 21 54.00 candles, and for eleven 

 months of the present year 19 84.100 candles. The average, as shown for 

 eleven month?, was reduced in consequence of the supply of English coal 

 during the first quarter being insufficient, from sea losses and failures on 

 contracts. 



Its purity has, throughout, been nearly perfect, so far as the usual im- 

 purities are referred to ; an occasional occurrence of them only has been 

 found, and then the cause could be traced easily. During a part of the 

 warm season of 1854, the high temperature of the pipes icithin the earth, 

 and that of the air and Cochituate water, has prevented the usual cooling 

 of the gas, and consequent condensation of vapors of benzole, naphtha, and 

 water, to the usual extent. Additional means having been secured, the 

 gas has lately been cooled, and the mains and secondary pipes have been 

 found to be clean. 



2d. " Its value in comparison with other gases on record." 



The experiments made almost daily have shown a mean value, during 

 the present quarter, of 22 80.100 candles. 



Xearly the whole of the gas supplied to the city of London, as appears 

 from the records published monthly, has the value of 13 to 13 8.10 candles, 

 while the cannel gas of Liverpool has been 22 candles. I have not ob- 

 tained the numbers denoting the value of the New York gas ; but from 

 frequent intercourse with the gentlemen testing the gas there, I conclude 

 that they have adopted the same standard as that chosen for Boston gas, 

 viz., about 20 candles. 



3d. "Are the burners in general use suited to the character of the gas? " 



Recent experiments, carefully conducted, seem to indicate that the com- 

 mon burners heretofore used in this country and in Europe are not adapted 

 to produce the most economical light from gas so rich as that supplied from 

 your works. The advantage arising from the use of the French burner, 

 with wide openings, has been fully proved in presence of distinguished, 

 scientific, as well as skilful practical men, and the subject, in their hands, 

 is likely to lead to improved applications. 



4th. " Is there any process, chemical or practical, in use here or else- 

 where, familiar to you, whereby Boston gas can be improved : " 



I deem the present arrangements made at your works the most 

 efficient which have been described, or are known to me. So far as they 



