42 Methods of estimating accurately 



result is a mixture of carbonates with magnesia, alumina, and iron, 

 if present. For strict accuracy, this must be wrapt up in thin paper 

 in one or more pellets, and transmitted to the top of a measure tube 

 full of mercury, where it is decomposed by a little muriatic acid, and 

 the gas given out measured. This is the whole of the carbonic acid 

 contained in the water, whether free or combined. The quantity of 

 the combined is afterwards ascertained in a different manner, and 

 being subtracted from this, the remainder is that which was free. 

 Should lime alone be in the water, the carbonate of lime precipitated 

 may be heated and weighed at once as carbonate, and from it the 

 equivalent of carbonic acid derived. This process is correct only 

 when the carbonic acid in the atmosphere is excluded from the free 

 lime in the flask. 



The sulphuretted hydrogen is known by adding solution of muri- 

 ate of copper in excess, filtering the precipitate from the liquid, and 

 washing it quickly, that it may not be oxidized by the air into sul- 

 phate of copper ; then putting it moist into nitro-muriatic acid, and 

 boiling till both the copper and sulphur present are dissolved. 

 Muriate or nitrate of barytes will after this give a precipitate of sul- 

 phate of barytes, from which the quantity of sulphuretted hydrogen 

 may be easily inferred. 



Ten thousand grains of the water should now be evaporated to 

 dryness, the residue heated to slight redness, and weighed to give 

 the whole saline contents of the water, as a check upon the amount 

 of the substances found individually. Thus also the silica, often pre- 

 sent, is separated. It will appear like bits of jelly towards the end 

 of the evaporation, and on moistening the dry mass with muriatic 

 acid, allowing it to stand for some time, and then boiling it in water, 

 the silica will remain insoluble. The solution separated from this 

 might serve subsequently for ascertaining the quantity of bases, but 

 as there is always a little loss in each operation, it is better, if there 

 is plenty of the water, to take a fresh portion. Some guess of the 

 quantity of animal or vegetable matters in the water may also be 

 now formed from that of the carbon which will probably be mixed 

 with the silica, and which will be burnt away in igniting it. To de- 

 termine these exactly, would require difficult and complicated pro- 

 cesses, which are not pretended to be here given. 



