^n Account of a ticio Eudiometer. 177 



fmall quantity of aeriform fluid (chiefly nitrous gas) * ; which, having no affinity for the 

 red muriate, or fulphatc, of iron produced, is gradually evolved, and mingled with the 

 refidual nitrogen. 



The impregnated folutlon with green muriate is more rapid In its operation than the fo- 

 lution with green fulphate. In cafes when thefe falts cannot be obtained in a flate of ab- 

 folute purity, the common or mixed fulphate of iron razy be employed. One cubic inch of 

 moderately ftrong impregnated folutlon is capable of abforbing five or fix cubic inches of 

 oxigen, in common procefles ; but the fame quantity muft never be employed for more 

 than one experiment. 



A number of' comparative experiments, made on the conftitution of the atmofphere at 

 , the Hotwells, Brlftol, in July, Auguft, and September, 1800, with phofphorus, fulphu- 

 rets of alkalies, and impregnated folution, demonftrated the accuracy of the procefles in 

 which the laft fubftance was properly employed. The diminutions given by the fulphurets 

 were indeed always greater by a minute quantity than thofe produced by phofphorus and 

 impregnated folutions: but the jreafon of this will be obvious to thofe who have ftudied the 

 fubjeft of Eudiometry. In no inftance was it found that 100 parts in volume of air con- 

 tained more than 21 of oxigen: and the variations connefked with different winds, and 

 different dates of temperature, moifture, &c. were too fmall, and too often related to 

 accidental circumflanccs, to be accurately noticed. 



In analyfing the atmofphere in different places, by means of impregnated folutions, I 

 have never been able to afcertain any notable difference in the proportions of its conftituent 

 parts. Air, collefted on the fea at the mouth of the Severn, on Oftober the 3d, 1800, 

 which mull have paffed over mu<^i of the Atlantic, as the wind was blowing (Irong from 

 the weft, was found to contain 21 per cent, of oxigen in volume; and this was nearly the 

 proportion In air fent from the coaft of Guinea, to Dr. Ueddoes, by two furgeons of 

 Liverpool. 



If we compare thefe refults, with the refults gained more than twenty years ago, by Mr. 

 Cavendifh, from experiments on the compofition of atmofpherical air, made at London 

 and Kenfington ; confidering, at the fame time, the refearches of Berthollet in Egypt and 

 at Paris, and thofe of Marti In Spain, we fliall find ftrong reafons for concluding, that the 

 atmofphere, in all places expofcd to the influence of the winds, contains very nearly the 

 fame proportions of oxigen and nitrogen , a circumftance of ^reat importance ; for, by 

 teaching us that the different degrees of falubrity of air do not depend upon differences in 

 the quantities of its principal conftituent parts, it ought to induce us to inilitute refearches 

 concerning the different fubftances capable of being diffolved or fufpended in air, which are 

 noxious to the human conftitution : particularly as an accurate knowledge of their nature 

 and properties would probably enable us, in a great meafure, to guard againft, or deftroy, 

 their baneful effects. 



• The decompofition of nitrous acid, by folutions containing oxide of iron, at its minimum of oxidation, 

 is a very complex procefs. The green oxide, during its convcrfion into red oxide, not only decompofes the 

 acid, but likewife afts upon the water of the folution ; and ammoniac is fometimes formed, and fmall por- 

 tions of nitrous oxide and nitrogen evolved with the nitrous gas. 



Vol. V. — August 1801. A a VI. 0» 



