476 An Account of a new Eudlometji', 



This elaftic fluid has been long known to confifl;<:hiefly of oxigen and nitrogen, mingled 

 together, or in a ftate of loofe combination, and holding in folution water. 



A variety of procefles have been inftituted with the view of determining the relative 

 proportions of the two gafes, but moft of them have involved fources of inaccuracy ; and 

 lately ail, except two (the flow combuftion of phofphorus> and the a£lion of liquid ful- 

 phurets), have been generally abandoned. 



, Both phofphorus and folution 6i fulphuret of pot-afh abforb the whole of the oxigen of 

 atmofpheric air at common temperatures, and they do not materially alter the volume, or the 

 properties of the refidual nitrogen; but their operation is extremely flow; and in many 

 cafes it is difRcult to afcertain the period at which the experiment is completed. 



I have lately employed as an eudiometricalfubftance the folution of green muriate, or 

 fulphate, of iron, impregnated with nitrous gas ; and I have found that it is in fome re- 

 fpe£ts fuperior to many of the bodies heretofore ufed, as it rapidly condenfes oxigen with- 

 out a£ling upon nitrogen ; and requires for its application only a very fimple and a very 

 portable apparatus. 



This fluid is made Ijy tranfmitting nitrous gas through green muriate, or fulphate, of 

 iron, difl"olved to faturation in water*. As the gas is abforbed, the folution becomes of a 

 deep olive brown, and when the impregnation is completed it appears opaque and almoft 

 black. The procefs is apparently owing to a fimple eleftive attraction; in no cafe is the 

 gas decompofed ; and under the exhaufted receiver it aflunjes its elaftic form, leaving -the 

 fluid with which it was combined unaltered in its properties. 



The inftruments neceflary for afcertaining the compofition of the atmofphere, by mean* 

 of impregnated folutions, conCft (imply of a fmall graduated tube, having its capacity 

 divided into one hundred parts, and greateft at the open end ; and of a vefliel for containing 

 the fluid. 



The tube, after being filled with the air to be examined, Is introduced Into the folution; 

 and, that the a£tion may be more rapid, gently moved from a perpendicular towards a 

 horizontal pofition. Under thefe circumftances the air is rapidly diminilhed; and, incon- 

 fequence of the dark colour pf the fluid, it is eafy to difcover the quantity of abforption. In 

 a few minutes the experiment is completed, and the whole of the oxigen condenfed by the 

 nitrous gas in the folution in the form of nitrous acid. 



In all eudiometrical procefles with impregnated folutions, the period at which the dimi- 

 nution is at a ftand muft be accurately obferved ; for, fliortly after this period, the volume 

 of the- refidual gas begins to be a little increafed, and, after fome houw, it will often fill a 

 fpace greater by feveral of the hundred parts on the fcalc of the tube, than that which it 

 occupied at the maximum of abforption. 



This circumftance depends upon the flow decompofition of the nitrous acid (formed 

 during the experiment), by the green oxide of iron, and the confequent produ£lion of a 



* Dr. Frieftley lirft obferved this procefs ; for a particular account of it, fee Refearches, Chemical and 

 Philofophical, page 152. Johnfon. 



3 fmall 



