COLLECTING GASES FROM WATER AND OTHER LIQUIDS. 2 75 



fine does not hold very firmly to the glass, and if used a 

 large piece must be taken, but if a mixture of one-half 

 paraffine and one-half wax be used, then a very little will be 

 found enough to sustain the pressure when passing the gas 

 through mercury into the graduated tubes. The end (a) 

 might have a stopcock of glass and the tube (b) might be 

 graduated, but I do not at present see many advantages in 

 that change, except under exceptional circumstances. If the 

 tube (6) should be long, it may happen that paraffine will 

 not melt in it until the surface of the water be a good deal 

 lowered, in that case either a shorter and wider tube may be 

 used, or if a great amount of gas be expected the long one 

 may be retained, and the melting of the paraffine assisted at 

 first by the application of a lamp. Very little help is 

 required in any case. 



On examining waters I find it useful to adopt this process 

 as a regular part of the analysis. As I intend to give a 

 separate paper on the amount of gas contained in waters, 1 

 shall say little about it at present, but may mention to shew 

 the importance of the subject that whilst a given portion of 

 the Manchester pipe water gave half a cubic inch of oxygen 

 gas, the same amount of water from a well near my labora- 

 tory, polluted by town drainage, gave only .025 of a cubic 

 inch, or in the proportion of 50 to 2J, shewing how tho- 

 roughly the organic matter had exhausted the soil of its 

 oxygen. 



As the process of collecting gases from water becomes by 

 this means perfectly simple, the apparatus may be employed 

 in many cases of the kind not here mentioned. For example, 

 the amount of carbonates in water may be obtained in this 

 way with great exactness, by simply adding some muriatic 

 acid to the upper receiver and boiling as described, after the 

 free gases have been removed. 



Sometimes hydrogen may be collected in this way from 

 dissolving metals, and estimated with advantage, instead of 



