SAMPLING A LIQUID 7 



is generated in the lower part of a room filled with air, being a 

 heavier gas it would naturally accumulate as a heavy liquid would 

 accumulate under a lighter one. A sample of the gas, therefore, 

 in a confined space of this kind would not be representative of the 

 whole contents unless previous to the sampling the whole were 

 subjected to violent stirring. An ordinary electric fan properly 

 placed in a room will within a short time so thoroughly mix its 

 gaseous contents that a sample may be drawn which will repre- 

 sent fully the character of the whole. 



In order that a sample of the gas may be unmixed and un- 

 absorbed, it is well that it should be aspirated into a vessel filled 

 with a liquid with which the gas is not miscible. Mercury, of 

 course, is the best liquid for this purpose for most gases, but on 

 account of its great weight and cost is unsuitable. As a rule, 

 water will be found entirely satisfactory for the aspirating mate- 

 rial, especially if the vessel be of considerable size so that the total 

 volume of gas drawn in is rather large. The small quantity of 

 gas which will be absorbed may be practically neglected. 



A very good sample of gas may also be secured by pumping 

 gas from any room or confined space into a dry rubber bag which 

 is previously completely flattened out so as to expel any air which 

 it may contain. In order that the last traces of air may be ex- 

 pelled, it is advisable in a case of this kind to fill the rubber bag 

 at least partially full of gas, remove it from the room where the 

 sampling is made, and express the contents, then carry back into 

 the room and refill. 



Gases may also be sampled into eudiometers or other vessels in 

 which the analytical processes are to be carried out. In all these 

 cases the study of the nature of the case, the experience of the 

 analyst and the character of the analysis will determine the meth- 

 ods which are best adapted to the purpose. 



ii. Sampling a Liquid. The sampling of liquid bodies is to be 

 accomplished in the same general way. A thorough stirring 

 of the liquid should always precede the sampling in order that 

 the sample may be uniform in character. The stirring may 

 be made either by mechanical means, as usually practiced, or, 

 if the liquid be one which does not contain a large amount of 



