1880.] 



On the Spectrum of Water. 



581 



gen as well as of hydrocarbons, burning in oxygen, and less strongly in 

 the flames of non-hydrogenous gases, such as carbonic oxide and cyano- 

 gen, if burnt in moist oxygen. Special pains were taken to purify 

 the gases from sulphur. The same spectrum is given by the electric 

 spark taken, without condenser, in moist hydrogen, oxygen, nitrogen, 

 and carbonic acid gas, but it disappears if the gas and apparatus 

 be thoroughly dried. We are led to the conclusion that the spec- 

 trum is that of water. The accompanying diagram, fig. 2, shows 



Fig. 2. 



the apparatus used for comparing the spectra of the spark in the gases, 

 dry and moist. The tube in which the sparks were passed was closed 

 at the end & by a quartz lens cemented to the glass ; c c were platinum 

 wires sealed into the glass. The gas was introduced through the 

 narrow tube a, provided with a branch closed by a glass stopcock. 

 The gas was passed from the gas-holder through two long drying-tubes, 

 of which the first was filled with calcium chloride, and the second 

 with phosphoric anhydride. The joints were all made with dry corks, 

 in order to avoid the hydrocarbons which contaminate gases passed 

 through rubber tubes. The exit-tube d was armed with a tube of 

 phosphoric anhydride, to prevent moisture entering that way. It was 

 necessary to pass a current of dry gas for fully an hour through the 

 warmed apparatus before the moisture was sufficiently expelled. 

 When this was done, photographs of the spark showed either no trace, 

 or only the faintest traces, of the spectrum above described. On now 

 introducing a drop of water through stopcock in the branch at a, and 

 letting it spread over a plug of asbestos placed in the tube at a, the 

 current of gas of course passed into the sparking tube moist instead of 

 dry ; and on now passing the spark, the spectrum above described at 

 once imprinted itself on the photographic plate. The effect w T as the 

 same, whether the gas used were hydrogen, oxygen, nitrogen, or car- 

 bonic acid. In the case of nitrogen, some of the channelled bands due 

 to that gas overlap the water spectrum, and partly obscure it, but not 

 so much but that it can be still very distinctly recognised. When a 

 condenser is used, the water spectrum disappears. The same spectrum 



2 s 2 



