SCIOPTICON MANUAL. 179 



to the cut, A is tho wrought-iron cylinder, B the cast- 

 iron cap, C the valve, D the nipple for hose, and E the 

 pressure-gauge. The hydrogen cylinder is coated with 

 vulcanized rubber and is proof against the action of 

 the sulphuric acid. It is usually a size larger than the 

 oxygen cylinder. 



" To operate the cylinder for oxygen, unscrew and remove 

 the cap; then set the cylinder over the fire (a range or 

 stove preferred) until quite warm and entirely dry ; then 

 pour in the chlorate of potash (one pound) and the black 

 oxide of manganese (four ounces). See that none of the 

 mixture falls upon the cylinder head, so as to prevent 

 the cap fitting closely down. Now rub a little tallow 

 on the cap to make a smooth joint, replace it so that the 

 marks on the cylinder and on the cap will coincide, and 

 screw the nuts down tight; then screw on the gauge 

 and open the valve. Allow the cylinder to remain on 

 the fire until the gas has come off, which will be indi- 

 cated by the rise of the colored fluid in the gauge. The 

 gas from one pound of chlorate of potash will raise the 

 fluid to within three-fourths of an inch to an inch of the 

 top of the tube. The cylinder ought not to be made 

 red hot in any part. When the gas has come off, set the 

 cylinder away to cool ; and after it has become cold, 

 shut the valve, remove the gauge, and screw on the 

 nipple. It is now ready for use at any time, but can 

 remain in the cylinder for months, if not required sooner. 



" When the gas is all used up, shut the valve, and let it 

 stay closed until you wish to make a new lot. This will 

 keep the cylinder dry and obviate the necessity of dry- 

 ing over the fire before recharging. Then, when you 

 wish to make fresh gas, unscrew and remove the cap, 

 tapping the end of the wrench with a hammer if the 



