58 DR. R. ANGUS SMITH ON THE EXAMINATION 



with excess of oxygen. Water in the first of these con- 

 ditions^ too^ may contain^ as I imagine^ the most dan- 

 gerous ingredients : germs of all diseases may exist in 

 such waters ; we do not know to what extent ; and, as we 

 are very ignorant on the subject, it is well to be alarmed at 

 the conditions, until we have examined them and made 

 distinctions. 



We do not know very much about the second of the 

 two ; and if I think it less dangerous, it is perhaps more 

 from a prejudice in favour of the abundance of vital air"^, 

 and of those hill-waters which do not contain bitter peat. 



^'Weighing the Organic Matter. 



^' If nothing apparently organic is seen, or if there be no 

 time to allow it to germinate, we may try the following 

 method. About half a gallon is boiled down in a platinum 

 vessel ; or it may be boiled in porcelain and transferred 

 with care, when only a few ounces are left, to a platinum 

 or even to a small porcelain capsule. The residue is dried 

 and weighed. It is then burnt so as to oxidize the carbon, 

 and weighed again; the difference gives the organic and 

 volatile matter of the residue. 212° F., or 100° Cent., is 

 not sufficient to remove all water ; but as it is a tempera- 

 ture so easily obtained, it is convenient to consider it 

 enough, especially as we cannot obtain the organic matter 

 by weighing with absolute exactness. We may obtain an 

 excess of water by the use of 212°, on one side ; 4)ut, again, 

 organic matter begins to be given off from some residues 

 even at that temperature; Professor Miller and others 

 advise about 300° F. It is at any rate well to state the 

 temperature in the account of the analysis. 



"The burning must not be effected at a very high heat, 

 or several salts will be decomposed or evaporated; but at 

 best some will suffer ; and the use of a little carbonic acid 



* The apparatus which I think most convenient for taking air out of 

 water, so as to estimate it, was described in the Memoirs of this Society. 



