OF ARTS AND SCIENCES. 



163 



through caustic potash bulbs, and then through a system of driers, 

 meeting successively calcic chloride, sulphuric acid, and phosphoric 



Fig. 8. 



pentoxide. It now enters the globe through the inlet tube reaching 

 to the bottom, carrying before it the hydrogen into the combustion 

 furnace. 



The water from the combustion was collected in a condenser, — the 

 details of whose construction are represented in Fig. 4, — which was 

 shielded from the furnace by a screen of asbestos paper. Nine tenths 

 of the water was condensed in the middle tube, and 

 all but the last traces of the aqueous vapor were 

 absorbed by the sulphuric acid through which the 

 air subsequently bubbled up at the bend of the U 

 tube, between glass beads, which broke the ascent 

 and divided the bubbles. With this condenser was 

 connected a U tube containing phosphoric pentox- 

 ide, which absorbed the last traces of the aqueous 

 vapor, seldom, however, gaining in weight more 

 than two milligrams during a combustion lasting 

 from seven to eight hours. Then follows a safety 

 tube containing calcic chloride (or in some cases 

 phosphoric pentoxide), to prevent any reflex diffu- 

 sion, and finally an adaptation of the principle of 

 Mariotte's flask to regulate the velocity of the air 

 current. It will be seen that the open mouth of the central tube of 

 this last apparatus dips under the mercury iu the tall jar, so that by 

 raising or lowering it the strength of the current could be exactly 

 regulated. 



Tig. 4. 



