BY DR. BURDON-SANDERSON. 313 



it should have a capacity of about 500 cubic inches (8193 c. c.). 

 Between the blower and the chamber is interposed a flask of 

 about 6 oz. capacity, through the cork of which two tubes 

 pass ; of these, one is prolonged nearty to the bottom ; the 

 other, the exit tube, ends just below the under surface of the 

 cork. This flask is filled with pumice, moistened with solu- 

 tion of potash. In this way the chamber is supplied with a 

 constant and perfectly steady stream of air, free from carbonic 

 acid. As, however, the quantity of air supplied by the blower 

 is much larger than is required, it must be diminished by 

 allowing a certain quantity to waste. For this purpose a T 

 tube is interposed between the blower and the potash flask, 

 the stem of which is connected by an India-rubber tube with 

 a kind of safety-valve, the construction of which is the same 

 as that of valve B, in fig. 251 ; the waste of air may be in- 

 creased or diminished by raising or lowering the longer of the 

 two tubes. The absorbing apparatus consists of two or a 

 greater number of absorption tubes (fig. 252), which are 

 charged with absorbing liquid. When each tube is placed at 

 its proper inclination, and the difference between the pressure 

 on opposite sides of the column of liquid is not too great, the 

 air, which enters the short limb by an end of India-rubber 

 tube which reaches nearly to the bend, passes up the long arm 

 in a regular succession of bubbles so small that it is thoroughly 

 acted on by the liquid. The two tubes are charged with a 

 solution of baryta, which in the longer is three times as strong 

 as in the shorter. The strengths of both solutions are deter- 

 mined volumetrically by a standrrd solution of oxalic acid 

 before and after every period of observation. 



Preparation of the Solutions of Baryta and Oxalic Acid. 

 Of the two solutions of baryta which are in use, the stronger 

 contains about 21 grammes of hydrate of baryta in a litre, 

 the other 7 grammes; the former is obtained by adding suf- 

 ficient distilled water to 420 cub. cent, of saturated baryta 

 water to make up a litre ; the latter contains 140 cub. cent, in 

 a litre. These liquids must be kept in bottles which have no 

 communication with the air, excepting through a flask or ab- 

 sorption tube filled with pumice, moistened with potash. The 

 oxalic acid solution must be prepared with the utmost accuracy. 

 It must contain 2.8636 grammes of pure well-crystallized 

 oxalic acid, free from efflorescence, in a litre. Before making 

 the solution, it is necessary to dry the crystals over sulphuric 

 acid for a few hours. The strength of this solution stands in 

 the ratio of exactly 1 to 22 to that of the ordinary volumetri- 

 cal solution of the pharmacopoeia. It keeps badly, being apt 

 to become mouldy, so that if a large amount is required, it 

 is better to keep the weighed quantities of oxalic acid than the 

 liquid. 



