AND RATIO OF TIIK.IR ATOMK" WKKiHTS. 21 



exhausted. Then the st()}>roek A was again closed, the tube eontaiuini;' tlie chlorate 

 was heated till the [>ressiu'e of the oxygen in it was nearly that of the atmosphere. 

 The stopcock li was then opened so as to permit a slow i)assage of oxygen into the 

 globe, the rate being determined nceording to the indieation of the gange a. 



15. PURITY OF TJIE OXYliKX eUKPARED FROM POTASSTtTM CIILOKATE. 



Oxygen prepared from chlorate might contain chloi'ine ; it might contain 

 nitroo-en which had not been removed from the appai-atus, or which entered it 

 during the experiment; oi' carbon dioxide produced by the combustion of organ ic 

 matter; or Hnel}- divided chlorate or chloi'ide; or the vapor of water. 



The vapor of water can be so completely removed that the remainder is 

 negligible. If the current is properly related to the dimensions of the drying tube, 

 sulphuric acid does not leave more than one milligramme in four hundred litres of 

 the gas.* The drying power of phosphorus pentoxide is yet greater, so that the 

 amount of water vapor left unabsorbed is perhaps not more than one hundredth part 

 as much as in the case of sulphuric acid.f If, as seems to be proved, a current of 

 three litres an hour is diied completely l)y a drying tube whose capacity is twenty- 

 five cubic centimetres, it may be safely assumed that a current at five times this 

 rate will be dried 1)y a tube five times as large. 



Cooke has observed that the desiccating power of phosphoric anhydride may 

 be lessened by the formation of a sort of glaze over the surface. The difficulty will 

 be overcome if the gas to be dried does not simply pass over the pentoxide, but 

 passes through a long column of it. If the pentoxide be so filled into the drying 

 tube that a channel can foi'ui, the difficulty would no doubt e.xist. But if the pent- 

 oxide is alternated with plugs oi- diaphragms of glass wool, between which it Hlls 

 the tube completely, the difficulty is removed. The initial deliquescence which 

 forms the glaze is long limited to the compartment first reached by the gas to be 

 dried; then at each diaphragm the current of gas spreads itself throughout the 

 whole ai'ea of the tube, and if the tube be pi'operly filled, it also spreads itself 

 throughout the whole area of the part filled with pentoxide except in the first com- 

 partment. But if no plugs of glass wool ai'e interposed, the channel which has 

 formed in this compartment gradually extends throughout the tube, and the gas is 

 no longer properly exposed to the action of the anhydride. 



Nitrogen was sought for by eudiometric analysis, as well as in other ways. 

 The maximum amount found was one twelve-thousandth, the minimum was about 

 five millionths; the mean was one thirty-thousandth. Since the densities of 

 * American Journal of Science, 30, 140. t American Journal of Science, 34, 199. 



