250 "Descrlpiion of an improved 



is necessary, by depressing the sliding-pipe any quantity of the 

 water may be let off at once into the lower vessel. By this means 

 a constant accession or diminution of the water is in the opera- 

 tor's power, without delay, or the assistance of a second person. 



I atn, sir, &c. 

 ^. Aikin, Esq. Secretary, John Cuthbert, 



^c. Philosophical Instrument-maksr. 



References to the Engravings, Plates IV. and V. 



Plate IV. (fig. I) is a view of the apparatus, as a blow-pipe 

 with the air vessel b thrown open to show the tubes within. 

 Through the tube dd, which descends within a quarter of an 

 inch of the bottom of the air-vessel, the air is conveyed from the 

 mouth. The tube e <? is to carry the air from the vessel h through 

 the jet to the lamp ; this tube contains another tube, which slides 

 air-tight into it, and is shown by fig. 6 ; to the extremity of this 

 a transverse tube (fig. 7) is connected. To the moveable one is 

 attached the jet ky which, by turning in an opposite direction to 

 that required when it is in use, is capable of shutting off the air, 

 as it becomes a stop-cock, by means of the hole h in the tube. 



The large tubey is to let the water down from the broad part 

 of the pneumatic trough, to force the air from the air-vessel 

 through the centre tube ee. 



The upper part of the tube dd is capable of being removed 

 to admit the pipe of the bladder (PI. V. fig. 6), which fits air- 

 tight into it, by which means oxygen gas may be forced into the 

 air-vessel (the common air being first displaced), which will 

 render the flame particularly effective where great heat may be 

 necessary. 



The lamp and tray / are placed on the cover of the blow-pipe, 

 so as to allow the wick to stand immediately before the jet. Tl^e 

 jet tube e can be raised or lowered for the purpose of depressing 

 or elevating the flame, as occasion may require ; tw is a shade 

 to prevent the breath from agitating the flame which is attached 

 to the tube d d, and may be removed back at pleasure. 



Fig. 3 is a section of the instrument in use, showing the water 

 descending from the upper part through the large tube into the 

 lower vessel b, and forcing the air above its surface through the 

 centre tube to the lamp. 



Fig. 2 is the apparatus employed as a pneumatic trough for 

 collecting gas, by means of the short sliding tube, shown in fig. 7, 

 which fits into the large tube J" (fig. 2), and is furnished with 

 the cap n (fig. 7) to prevent the water being thrown over the 

 upper edge of the trough when forced up from the air-vessel, by 

 Jjlowing through the tube d (fig. 1). 



Fig. 8 



