SIR ANDREW NOBLE: RESEARCHES ON EXPLOSIVES. 205 



subdivided into tenths by eye estimation. Errors of parallax are avoided by the use 

 of a mounted lens sliding on the rod E, and the corrections are thus read directly in 

 percentages as easily as the temperatures would be read by means of a thermometer. 



Absorptions are carried out in separate pipettes, one of which is shown in position. 

 About 20 cub. centims. of the absorbent is usually confined over mercury in the 

 bulb E, which is slightly inclined in order to facilitate the return of the unabsorbed 

 gas. The horizontal bulb D receives the mercury displaced by the gas. The bulb F 

 contains clean mercury, and, like the bulb E, can be placed in communication with 

 the capillary G by means of the three-way stop-cock H. 



The explosion pipette resembles that of DITTMAR, but has a three-way stop-cock 

 and mercury bulb arranged as in the absorption pipettes. 



In conducting an analysis, the sample tube is connected to the measuring tube by 

 means of a capillary tube previously filled with mercury, and the gas drawn in by 

 lowering the reservoir. After the mercury has been roughly levelled, the stop- 

 cock N is turned so as to connect the capillary K with the tube U, and an absorption 

 pipette, containing caustic potash solution, connected to the measuring tube by 

 means of thick- walled rubber tubing, the ends of the capillaries being made to meet. 

 A little water is then sucked through the capillaries into the bulb F, and mercury 

 allowed to run back and fill the capillaries. The stop-cock leading to the large 

 mercury reservoir having been closed, and the level tube being open to the atmo- 

 sphere, the mercury is accurately levelled, as already described, and the volume ol 

 the gas read by means of the reading telescope. A reading of the correction tube is 

 also taken. 



In order to determine the amount of carbon dioxide present, the gas is driven over 

 into the absorption pipette, followed by sufficient mercury to clear the capillaries, and 

 the pipette well shaken in order to make the absorption complete. A little more 

 mercury is then run over in order to clear away the potash from the bottom of the 

 capillary attached to the absorption bulb, and the stop-cock N reversed so that the 

 mercury in the capillaries runs into the tube U. The stop-cock N is then again 

 turned and the gas slowly passes into the measuring tube, the rate being controlled 

 by the stop-cock H, which is reversed as soon as the absorbent reaches it, so that the 

 gas may be swept out of the capillaries by means of clean mercury from the bulb F. 

 The stop-cock N is closed as soon as it is reached by the mercury. The gas is again 

 carefully measured and the decrease of volume (after the correction for alteration of 

 temperature and pressure has been applied) is equal to the amount of carbon dioxide 

 originally present. The residue is then treated with alkaline pyrogallol, in order to 

 ascertain whether any trace of air has been left in the connecting tubes during the 

 collection of the sample and has so contaminated the gas. (This is more likely to 

 occur when the explosion has taken place under feeble pressures and but little gas 

 been produced.) If any oxygen is absorbed by the pyrogallol, its volume is multiplied 

 by 4 '8 and the product (representing the volume of air present) deducted from the 



