Dittmar’s Nitrogen. An amount of water, about half that taken for the carbon, is evaporated in a similar way. The residue is transferred to a large copper or silver boat, and mixed with about 50 grains of soda made from pure sodium, or with a mixture of soda and baryta, and burnt in a stream of hydrogen in a short combustion tube, which is closed in front by a nitrogen absorption bulb charged with exceedingly weak acidulated water. The amount of ammonia given off is estimated by the Nessler test as described under “Ammonia.” Subtracting the amount of inorganic ammonia the residue multiplied by 14⁄17 yields the quantity of organic nitrogen in that volume of water.
A few blank experiments must be made to observe and allow correction for the amount of experimental error.
Carbon method of Drs Dupré and Hake.[261]—This method appears to be very accurate, but it necessitates a number of minute precautions, which cannot here be particularised. A residue is obtained by evaporating the water either in the ordinary hemispherical glass dish, or in an exceedingly thin silver one, which after being ignited is supported in a platinum hemisphere of convenient size. At the close of the evaporation this dish is crumpled up without being handled and introduced into a combustion tube, similar to that described under Dittmar’s process. The carbonic acid is absorbed in bright baric hydrate solution, and the precipitated baric carbonate is, with suitable precautions to prevent access of impure air, collected on a filter and washed. It is dried and weighed. The result divided by 19·4 gives the weight of organic carbon. As another method of estimating the carbon the authors propose to compare the turbidity produced by the carbonic acid evolved from the combustion of the residue in solutions of basic acetate of lead with that produced by known quantity of carbonic acid.
[261] ‘Chem. Soc. Journ.,’ March, 1879.
Pres. The preservation of rain water in a state of purity necessitates the greatest care in constructing the tanks, especially if the latter are underground. Of eight samples of stored rain water examined by the River Commissioners only one was fit for domestic use, the others were all polluted by animal matter. Storage room sufficient to hold 120 days’ supply will be found sufficient for the driest district. The small cisterns for service water should not be placed in positions where it can receive the emanation of water closets or sleeping apartments. They should be frequently cleaned out. The best are made of enamelled slate or properly painted iron. Wherever possible a water service should be on the constant supply system.
For wells the chief precaution necessary is to keep out surface and drainage water by maintaining the walls water-proof for a considerable depth. On shipboard water is preserved in iron tanks or in casks well charred on the inside. Water cannot be safely kept in copper or leaden vessels, and it receives a calcareous impregnation by contact with lime, mortar, slate, or stone containing lime. The addition of 1⁄2 to 1 per cent. of finely powdered binoxide of manganese materially promotes preservation, especially at sea, where the motion of the vessel and the subsequent agitation of the water increases the points of contact. Water never putrefies in iron vessels or when some fragments of metallic iron are immersed in it. Distilled water should be preserved in glass bottles or carboys. See Lotion, Spirits, Water, Distilled Eye water, Perfumed water, and the articles below.
Water, Soda. Each bottle of this liquid should contain at least 15 grains of carbonate of sodium, but that of the shops is usually nothing else but water highly charged with carbonic anhydride. Not a particle of soda enters into its composition, on which account it cannot be substituted for the preparation of the Pharmacopœias.
To produce a superior article of soda water, the possession of a powerful aërating and bottling machine is absolutely necessary. The water employed must also be of the purest quality, the carbonic anhydride well washed with water, and the corks so prepared that they will not impart their peculiar flavour to the beverage. See Powders, Solution, Wines, and Lead in Aerated water.
Water, Tar. See Infusion of Tar.
WATERS (Distilled). Syn. Aromatic waters, Odoriferous w., Perfumed w.; Aquæ (Ph. L.), Aquæ destillatæ (Ph. E. & D.), L. Pure water, charged, by distillation, with the volatile, odorous, and aromatic principles of plants.