Measurement of High Temperatures. 337 



on its surface the gases with which it comes in contact. The 

 perusal of M. Edmond Becquerel's last paper has suggested the 

 experiments which led* us to the discovery of the real reason why 

 platinum is not to be trusted' when we wish to try experiments on 

 gases or vapours at a high temperature. 



We take a platinum tube made from a well- worked ingot *, 

 which is joined and drawn like a wire, so as to give a very 

 sound, perfectly homogeneous tube, without any soldering. (The 

 two tubes upou which we experimented were in this state, and 

 had been made with the utmost care by MM. des Moutis, Cha- 

 puis and Quennessen.) This tube is introduced into another 

 of Bayeux porcelain much wider and shorter, and the annular 

 space between the two is closed by means of corks. This annular 

 space is filled with broken porcelain, and a current of dry pure 

 hydrogen is sent through it, which, entering and issuing by two 

 glass tubes, cannot have any direct communication with the 

 inside of the platinum tube. This tube, which is closed by two 

 india-rubber stoppers previously heated, receives air which has 

 been dried by passing through an Alvergniat's washing-bottle 

 (laveur de M. Alvergniat), a glass filled with pumice moistened 

 with sulphuric acid, and, lastly, a vessel with pieces of fused pot- 

 ash. The apparatus thus preparedf is put into a furnace fed 

 with air and carbon from gas-retorts. Thus in our apparatus 

 the air and hydrogen circulate separated by a solid and con- 

 tinuous partition of platinum. On collecting the air which 

 leaves the platinum tube at the common temperature, it is found 

 to have the normal composition — 



Oxygen . . . 20*9 21 



Nitrogen ... 79' 1 79 



100-0 100 



At the ordinary temperature the hydrogen which issues from the 

 annular space is entirely absorbed by oxide of copper without 

 residue. 



But if the temperature is slightly raised, the effect alters with 

 surprising regularity : the air gradually loses its oxygen, and 

 there condenses in the delivery-tube water which we have col- 

 lected and weighed; its proportion keeps increasing with the 

 temperature. At last, when this has reached about 1100° (by 



* We are only speaking here of common spongy platinum made coherent 

 by hammering in the way that it has always been prepared until lately. We 

 are now having a tube made of cast platinum, with which we shall repeat 

 our experiments. 



t This is the same apparatus which one of us has already used, except 

 that a tube of porous earthenware was then employed instead of the plati- 

 num tube (see Comptes Rendus, vol. lii. p. 524). 



