ON WATER ANALYSIS. 
377 
the ammonia. By this means, the whole of the nitrogen originally introduced 
into the water is valued with considerable accuracy ; and a distinct estimate is 
made of the nitrogen which has been rendered innocuous by oxidation, and of 
that which still exists in the condition of putrescent or putrescible organic ma¬ 
terials. 
The first step, then, in the analysis, is the determination of the carbon and 
nitrogen in the residue left by a given quantity of water. These determinations 
are made in one operation, and by a process of combustion somewhat similar to 
that employed in the analysis of organic compounds. As, however, a water re¬ 
sidue invariably contains carbonates, it becomes necessary to get rid of them— 
that is, to expel the carbonic acid by some previous process which at the same 
time should have no effect upon the organic matter—as, for instance, by the 
expulsion of volatile organic acids, etc. With this view, boracic acid was at 
first tried, but with unsatisfactory results. Subsequently, sulphurous acid was 
employed, and with great success. This substance decomposes the carbonates, 
does not act injuriously upon the organic matter, and possesses the further ad¬ 
vantage of destroying and eliminating the nitrates and 
nitrites. The residue left by a water, therefore, to which 
sulphurous acid had been added previously to evapora¬ 
tion, contains the nitrogen of the organic matter, and 
also that of the ammoniacal salts present. By a separate 
estimation of the latter, and subtracting the amount from 
the quantity found by the combustion, we arrive at the 
numbers expressing the “ organic nitrogen.” 
The mode of proceeding is as follows :—1 litre of 
water is mixed in a flask, the mouth of which is closed 
by a watch-glass, with 15 c.c. of a saturated solution of 
sulphurous acid in distilled water; the mixture is heated 
to boiling for a few minutes, and then, having been 
emptied into a hemispherical glass bowl, it is evaporated 
carefully to dryness, being maintained for a short time 
at the end at the temperature of 100° C. A small quan¬ 
tity of chromate of lead is then mixed with the residue, 
and the whole transferred to a combustion tube, (about 
the length usually employed in the combustion of non- 
nitrogenous organic substances,) rinsing in carefully with 
oxide of copper, with which the tube is nearly filled, leav¬ 
ing space for the introduction of a short coil of reduced 
copper. The open end of the combustion tube is then 
drawn out, bent twice at right angles, and carefully con¬ 
nected, by caoutchouc tubing securely wired round, with 
the side tube of a Sprengel vacuum apparatus. 
This instrument which has proved of so great value in 
the hands of several chemists, particularly the Master of 
the Mint, consists, in its simplest form, as shown in the 
annexed sketch, of a funnel, /, containing mercury, and 
continued below by a tube which can be closed near its 
upper end by a compression cock, c, whilst a little lower 
down is an arm projecting laterally. As soon a3 the stop¬ 
cock at c is opened, the mercury falls down from the 
funnel, and in falling carries with it air derived from 
the branch tube. If this latter is connected with a 
closed vessel, exhaustion takes place; the whole length 
of the vertical tube being filled with alternate cylinders 
of mercury and air, having a downward motion. When the exhaustion is 
