98 OPTICAL PROJECTION 



0*917 to 0*920. Heavier ether owes its density to alcohol and 

 water. Only the ether being vapourised at the end of an 

 exhibition, that which remains is of inferior quality, and will 

 saturate the gas less perfectly. It must always be poured 

 out of the tank at the finish, and if the quantity be not large, 

 the safest plan is to throw it away. It may, however, be kept 

 (separately) and used with fresh ether once or twice. After 

 twice, I consider the residue should be rejected. Petroleum 

 ether certainly has the advantage in this respect. Either 

 must be stored in as cool a place as can be found. 



No tap or connection having to do with ether vapour can 

 be lubricated with any kind of grease, as the ether rapidly 

 dissolves it. Connections may be screwed up gas-tight with 

 soap, or washers of leather and soft lead. Taps may be 

 lubricated with vaseline. Rubber tubes are also acted upon, 

 and should be, therefore, of the thickest and best, and as 

 short as possible, placing the generator on the table, if one 

 is used. Any heat from the lantern will promote satura- 

 tion. 



Large nipples cannot be used with sulphuric ether, the jet 

 * snapping ' with them. The aperture should not exceed 1 mm. 

 bore. This of course limits the light, though it is nearly equal 

 to the oxy-hydrogen jet of the same bore. 



The connections are easily understood. The tube from the 

 oxygen supply is divided into two at a T or Y joint. One 

 branch of this goes to the oxygen nozzle of the jet or dissolver, 

 the other to the ingress end of the generator. There should 

 be at least six inches from the fork of the Y to the generator, 

 and there must be a stop-cock between them. From the egress 

 end of the generator a nozzle, also furnished with a stop-cock, 

 goes to the hydrogen nozzle of jet or dissolver. Every con- 

 nection should first be made with all taps turned off, and the 

 bag duly weighted. The bag or the cylinder is then turned 

 on, the latter with a regulator of course ; next, the tap between 

 the fork and the generator. Finally we turn on the hydrogen 



