The separation of ammonia from most other volatile substances may be best effected by means of the bichloride of platinum.
Small quantities of ammonia are determined by the " Nessler test." A standard solution of ammonium chloride is prepared, and a certain portion being measured into a suitable cylindrical vessel, in a similar glass is poured a portion of the ammoniacal fluid to be examined ; equal portions (2 c.c.) of the Nessler reagent is added by means of a small pipette to the contents in the two tubes, when, if the same tint is struck in the two fluids, the amounts of ammonia present are equal ; if the tints are not equal, the standard solution may be diluted, or made stronger if required, and again tested, until the tints exactly match each other. An important condition is that no precipi tate must take place ; if the ammonia present in the liquid to be tested be so large as to give a precipitate, it should be diluted to some equi-multiple of its original bulk. The matching of tho tints being performed as before, the amount of ammonia present must be obtained by multiplying the quantity contained iu the etandard solution by the degree or number of times to which the dilution has been carried.
Dr. Wunklyn has proposed an ingenious method of determining the amount of organic contami nation in water by the Nesslcr test, which commends itself more especially, as it can be performed by any person who can fairly conduct a delicate chemical test.
The increased consumption of ice cannot be regarded with indifference by our medical authori ties, when wo consider the immense amount of nitrogenized impurities which are sometimes met with in this article when used as an article of consumption.
A measured quantity of the water or dissolved ice is first distilled, and the distillate collected which will contain the free ammonia. Waoklyn uses 500 c.c., and collects the first 50 c.c. of distillate for Nesslerizing; the succeeding 150 c.c. are collected and thrown away. A mixture of caustic potash and permanganate of potash is then added to the residue in the retort, and the dietillation again proceeded with, and each 50 c.c. of the distillate is collected until 150 c.o. have
passed over ; each of these is Nesslerized, and the quantities of standard ammonia-solutiou used to match the tints added together for the amount of " albuminoid " ammonia.
Tho mixture of caustic potash and permanganate is made by dissolving 200 grammes of potash and 8 grammes of crystallized permanganate of potash, so that the solution is equal to 1 litre. 50 c.c. of this solution is required for each analysis.
In this latter part of the process, the nitrogenized principles, whether animal or vegetable, which may be contained in the liquid is oxidized, and ammonia is obtained as a product of the decompo sition.
A great deal of acrimony has unfortunately been introduced into the dismission of the merits of this process, and though'perliaps it may not satisfy the requirements of a strictly scientific inquiry, it certainly may lay claim to this important and useful function, that a contaminated water could never be allowed to pass without condemnation. On the other hand, a water which may be quite harm less is made to take a suspicious character as regards its sanitative merits. To an individual of a highly nervous temperament, this may be as great a source of trouble as if the water were decidedly contaminated.
Pryaration of the " Nessler Reagent" for Ammonia.—Dissolve 82.5 grm. of potassic iodide in about 250° e.e. of distilled water, and add gradually a cold saturated solution of corrosive sub limate until the mercuric iodide precipitated ceases to be re-dissolved on stirring; continue adding drop by drop until a slight precipitate remains undissolved. Dissolve 150 grm. of solid hydrate in 150 e.e. of distilled water ; allow the solution to cool, and add it gradually to the above solution, and make up with distilled water to one litre.
On standing a brown precipitate is deposited, and the solution becomes clear and of a pale greenish-yellow colour. It is ready for use as soon as it is perfectly clear, and should be decanted into a smaller bottle, as required.