23 



C. COLLECTIONS OF APPARATUS SPECIALLY ARRANGED FOR 



INSTRUCTION. 



APPARATUS FOR SPECIALLY IMPORTANT ILLUSTRATIONS. Nos. 

 107 to 126. (Similar collections are lent by tlie 

 Department to teachers of Science Classes.) 



107. Apparatus to decompose steam by a stream of 

 electric sparks. 



E. 52. 1874. 



Consisting of a five-cell Grove's battery, a Ruhmkorff coil, a 

 globe fitted with platinum wires for the passage of the spark, and 

 a leading tube for gas, mounted upon a flask, in which to generate 

 steam. The flask is half filled with water, which is made to boil, 

 and the steam driven slowly through the globe, led into the 

 pneumatic trough, and condensed. When the air is completely 

 displaced from all parts of the interior, the platinum wires are 

 connected with the coil, which is then set in action. A portion 

 of the steam passing through the globe is thus decomposed, and 

 the mixed oxygen and hydrogen gases can be collected over the 

 pneumatic trough. 



108. Apparatus for gas analysis. 

 E. 53. 1874. 



Intended to submit a mixture of gases to the successive 

 action of absorbents, and so to determine its composition 

 volumetrically. The modus operandi, divested of minor details, 

 is simply this. The gas to be analysed is placed over mercury 

 in the reservoir I, then drawn by the descent of a column 

 of mercury into the measuring tube C, where its volume 

 is determined. Being returned into the reservoir I, into 

 which an absorbing agent is thrown, which deprives it of 

 one constituent, the gas is brought back to the tube C and 

 measured again, and this process is repeated until the com- 

 position of the mixture is ascertained. An equable tem- 

 perature is maintained iu the measuring tube G by the 

 vessel H being filled with water, which can be agitated, if 

 necessary. The pressure is regulated by the mercury cistern B, 

 which is raised or lowered as may be necessary, and it is 

 measured by the column of mercury in the tube A. 



Instructions for using the Apparatus. 



Let the gas to be analysed be common air, or the gas evolved 

 by ebullition from natural waters, consisting usually of carbon 

 dioxide, oxygen, and nitrogen. First, the gas is carefully 

 transferred without loss to the jar I, and thence drawn by 

 lowering the mercury reservoir and opening the stopcocks into 

 the tube C, where the apex of the mercury is brought to coincide 



