140 Shiro Tashiro 



gas taken from the respiratory chamber, since the pressure in A and 

 B is kept equal to the atmospheric during the transfer. 



One now watches the surface of the drop at F with a lens to see 

 whether any formation of barium carbonate occurs within ten minutes. 

 With this apparatus, I have repeatedly introduced accurately known 

 quantities of carbon dioxide of very high dilution into B in the manner 

 just described and as a result have found, with remarkable regularity, 

 that i.o X io~ 7 gram of carbon dioxide is the minimum amount 

 which will cause a formation of barium carbonate within a period of 

 ten minutes. Smaller amounts of carbon dioxide give no visible 

 results; while larger amounts give a deposit more rapidly, and appear 

 in larger quantities. This minimum detectable amount 'i.o X io~ 7 

 gram is about the amount which is contained in J c.c. of natural air, 

 in which we assume 3.0 parts of carbon dioxide in 10,000 by volume. 9 



In order to determine the concentration of carbon dioxide in the 

 respiratory chamber, one must first find, for the apparatus used, the 

 minimum detectable amount of carbon dioxide. Then one finds, by 

 trial, 10 the minimum volume of gas necessary to give the first visible 

 formation of barium carbonate. This volume must, therefore, con- 

 tain the known minimum detectable amount of carbon dioxide. From 

 the ratio between this volume and the original volume of the respira- 

 tory chamber, out of which this amount is withdrawn, the absolute 



9 LETTS and BLAKE: Proceedings of the Royal Dublin Society, 1899-03, ix, 

 p. 107. 



10 In the case of biological problems, when the specimen gives off carbon 

 dioxide continuously, and sometimes at different rates, varying with the time, it 

 is much simpler not to attempt to determine the minimum volume by a continuous 

 trial with the same sample; but instead to repeat the experiments with a series 

 of samples of known weights for a known time, and determine the minimum 

 volumes which give the precipitates, and the maximum volumes which do not 

 give the precipitates. In this way, it can easily be calculated what is the mini- 

 mum volume which gives the precipitate for the given weight of the specimen for 

 a given time. Table I on page 1 14 will illustrate this more clearly. 



Another upturned cup H provided in the respiratory chamber A is used in 

 case only the qualitative detection of C0 2 is wanted. In such a case, the perfectly 

 clear barium hydroxide solution is introduced, after the necessary cleaning and 

 washing, to the respiratory chamber, forming the usual drop at H instead of F. 

 It should be noted that in case a smaller capacity is necessary for the respiratory 

 chamber, the mercury is introduced by a pipette to the bottom of the chamber 

 at K. 



