METHOD OF DETEIJMIXIXJ MOLECULAR WEIGHTS. 99 



the only difficiiJt\' which lies on tlic way is the exact deteiiinriation 

 of the boiling points, as has ah-eady been pointed out by Beckmann. 

 Irregular boiling and bumping, attended with sudden alterations in 

 the temperature of a boiling livpiid are phenomena which are too well 

 known to be mentioned. Even when the liquid seems to be regularly 

 boiling, there are still constant changes in the temperature of the 

 li<]uid, as may be readily observed by the use of a delicate thermo- 

 meter. A'arious means have been tried to overcome these difficulties. 

 ]5its of metallic wire or foU, of broken glass, etc. are almost useless. 

 JJaoult tried coating the thermometer bulb with a layer of palladium 

 recently charged witli liydrogen gas, but it did not lead to the 

 desired result, as the evolution of hydrogen gas soon slackened and, 

 in about 20 minutes, stopped altogether. 



Beckmann has succeeded in gi-eatly overcoming the difficulties. 

 He uses a piece of stout platinum wire which is fixed in the bottom of 

 tlie boiling vessel l)y means of fusible glass. On account of the 

 superior thermal conductivity of tlie metal, the boiling is said to take 

 place exclusively from the piece of platinum, and bumping is avoided 

 entirely. I regret to say that I have not yet had an experience witli 

 Beckmann'« apparatus. In fact, we ordered one from Germany, but 

 on my first attempt to make trial of it, the boiling vessel was found 

 t(j be cracked at the point of insertion «jf the platinum. Tliis was 

 merely an accident, but it is an accident wliich nray often occur. A 

 small p(jrlion of the bottom of the boiling vessel is thickened by the 

 insible glass, and there is no wonder if the bottom is cracked by the 

 slightest carelessness in heating. 



Tiie means wliich I adopt in producing a constant temperature 

 in tlie boiling li(juid has already been described in my paper, on " The 

 delerminati(jn of the temperature of steam arising from boiling salt 

 solutions," and consists in ])assing a current of the vapour of the 



