of Determining Moisture and Carbonic Acid in Air. 313 



aspiration has (for reasons given, p. 321) been about 1 litre 

 per minute. The following were test experiments with faster 

 rates : — 



Experiment No. 7. 



25 litres aspirated at 3 litres per minute. 



Pair (1) . . . . +0-2012. 

 Pair (2) . . . . +0*0004. 



Experiment No. 8. 



25 litres aspirated at 4 litres per minute. 



Pair (1) . . . . +0*3453. 

 Pair (2) .... +0-0003. 



Experiment No. 9. 

 21 litres aspirated at 7 litres per minute. 



Pair(l) .... +0-2142. 

 Pair (2) .... +0*0001. 



The rate of aspiration may thus be, if required, 7 litres per 

 minute. 



With the view of determining whether there is any appre- 

 ciable constant error due to incomplete absorption of moisture 

 by the first tube, we have added up the variations in weight of 

 the second tube in all our experiments in which a second 

 absorption-tube was used. 



Total moisture absorbed Sum of variations 



by first tube. of second tube. 



13-0522 grms. -0*0007 grms. 



The mean variation in weight of the second tube was thus 

 only 0*0065 per cent. ; and a constant error of this order would 

 be quite inappreciable in ordinary experiments. 



Additional evidence of the accuracy of the method is afforded 

 by the fact that in the simultaneous determinations recorded 

 below (pp. 322 and 327) the two sets of results are practically 

 identical. We have also made for another purpose two ex- 

 periments in which air dried by sulphuric acid was passed 

 through a weighed vessel containing water, and then again 

 through a drying apparatus. The apparatus used was on a 

 much larger scale, and the rate of aspiration was in one case 

 7 and in the other 15 litres per minute. The balance em- 

 ployed weighed to centigrammes. The vessel containing water 

 lost 4*86 and 3*62 grammes, and the drying vessels gained 

 4*86 and 3*61 grammes respectively. 



If the modified method described above be compared with 

 the old method as investigated by Shaw, it is seen that by the 



