JUXE 28, 1895.] 



SCIENCE. 



707 



the remaiuiug nitrogen is consumed, so 

 that, finally, the working vessel is charged 

 with a mixture of argon and oxygen only, 

 from which the oxygen is removed by ordi- 

 nary well-known chemical methods. I 

 may mention that at the clo.«e of the opera- 

 tion, when the nitrogen is all gone, the ai-c 

 changes its appearance and becomes of a 

 brilliant blue colour. 



I have said enough about this method, 

 and I must now pass on to the alternative 

 method which has been very successful in 

 Professor Eamsay's hands — that of absorb- 

 ing nitrogen by means of red-hot magne- 

 sium. By the kindness of Professor Earn- 

 say and Mr. Matthews, his assistant, we 

 have here tlie full scale apparatus before us 

 almost exactly as thej- use it. On the left 

 there is a reservoir of nitrogen derived 

 fi'om air bj- the simple removal of oxygen. 

 The gas is then dried. Here it is bubbled 

 through sulphuric acid. It then passes 

 through a long tube made of hard glass and 

 charged with magnesium in the form of 

 thin turnings. During the passage of the 

 gas over the magnesium at a bright red 

 heat, the nitrogen is absorbed in a great 

 degree, and the gas which finally passes 

 through is immensely richer in argon than 

 that which first enters the hot tube. At the 

 present time jou see a tolerably rapid bub- 

 bling on the left, indicative of the flow of 

 atmospheric nitrogen into the combustion 

 furnace ; whereas, on the right, the outflow 

 is verj- much slower. Care must be taken 

 to prevent the heat rising to such a point 

 as to soften the glass. The concentrated 

 argon is collected in a second gasholder, 

 and afterwards submitted to further treat- 

 ment. The apparatus employed by Profes- 

 soi- Kamsay in the subsequent treatment is 

 exhibited in the diagram, and is very eft'ect- 

 ive for its purpose; but I am afraid that 

 the details of it would not readily be fol- 

 lowed from any explanation tliat I could 

 give in the time at my disposal. The prin- 



ciple consists in the circulation of the mix- 

 ture of nitrogen and argon over hot mag- 

 nesium, the gas being made to pass round 

 and round until the nitrogen is elTectively 

 removed from it. At the end that opera- 

 tion, as in the case of the oxygen method, 

 proceeds somewhat slowly. When the 

 greater part of the nitrogen is gone, the re- 

 mainder seems to be unwilling to follow, 

 and it requires somewhat protracted ti-eat- 

 ment in order to be sure that the nitogeu 

 has wholly disappeared. When I say 

 ' whollj- disappeared,' that, perhaps, would 

 1)6 too much to say in any case. What we 

 can say is that the spectrum test is ade- 

 quate to show the presence, or at any rate 

 to show the addition, of about one-and-a- 

 half per cent, of niti'Ogen to argon as pure 

 as we can get it ; so that it is fair to argue 

 that any nitrogen at that stage remaining 

 in the argon is only a small fraction of one- 

 and-a-half per cent. 



I should have liked at this point to be 

 able to give advice as to which of the two 

 methods — the oxygen method or the mag- 

 nesium method — is the easier and the more 

 to be recommended: but I confess that I 

 am quite at a loss to do so. One difticulty 

 in the comparison arises from the fact that 

 they have been in different hands. As far 

 as I can estimate, the quantities of nitrogen 

 eaten up in a given time are not very dif- 

 ferent. In that respect, perhaps, the mag- 

 nesium method has some advantage ; but, 

 on the other hand, it may be said that the 

 magnesium process re<iuires a much closer 

 supervision, so that, perhaps, fourteen hours 

 of the oxygen method may not unfairly 

 compare with eight hours or so of the mag- 

 nesium method. In practice a great deal 

 would depend upon whether in any partic- 

 ular laboiatory alternate currents are avail- 

 able from a public supply. If the alternate 

 currents are at hand, I think it may probably 

 be the case that the oxygen method is the 

 easier; Ijut otherwise, the magnesium 



