SOME GENERAL HINTS ON TESTING.

New Zealand Mail, Issue 1211, 17 May 1895, Page 7

SOME GENERAL HINTS ON TESTING.

A correspondent of that useful little English paper, Farm , Field and Fireside having asked for instruction how to analyse and test milk and water so as to ascertain the constituents of these substances, another correspondent supplies the information which appears below and which we think will be of interest to a good many New Zealanders : —You ask for instructions how to analyse and test water, milk, etc., so as to ascertain the constituents of these substances. This is a very large order, and to execute it properly the editor would require another double number. Your best plan is to get some books on experimental chemistry—-a cheap one that would suit you admirably is “ Church’s Laboratory Guide for Agricultural Students,” published at 6ai 6d by Gurney and Jackson, Paternoster How, London. I give you a few tests for water, principally taken from that work. (1) Evaporate one ounce of water to dryness just in a porcelain basin, and note the character of the residue. It should be very small, colourless and odourless. (2) If ammonium oxalate solution is added to water, and a white precipitate is formed, yon may be pretty certain that the water contains lime. (3) Fill a test tube half full of water, and add 20 drop 3 nitric acid and 5 drops of a 5 per cent, solution of silver nitrate; if a white precipitate falls, chlorides are indicated. (4) Add 10 drops of hydrochloric acid and 10 drops of a 10 per cent, solution of barium chloride to water,'half filling a test tube ; a white precipitate indicates sulphates. (5) Add five drops of “ Nessler’s test” to auother test tube half filled with water; a brown or yellow colour indicates ammonia. I give you these tests as a sample; for you must go to the book itself or a similar work. Hardness in water is usually determined by Clark’s test, which is a solution of soap in weak spirit, and by a solution of chloride of calcium. It is impossible to here explain the procedure, and special apparatus is required. It may be sufficient to say that 67 drops of distilled water would require 1 drop of the standard soap test to produce a permanent lather, and the degree of hardness is calculated from the excess of soap test (over 1 to 67) required to produce a permanent lather. There are several ways of testing milk in an expeditious manner, the “ ListerBabcock ” (Lister and Co., Dursley) is ingenious and fairly reliable, but for accuracy, chemical analysis must be resorted to. The total solids are found by thoroughly drying the milk and weighing the residue. The solids, not fat, are ascertained by a somewhat similar process during which the fat is removed by exhaustion with dry ether, or petroleum spirit. More accurate results are obtained by Adams’ paper coil method, which cannot be described here. The albuminoids may be found bv a soda-lime combustion. But I daresay you will see by this time that to analyse water or milk expensive apparatus and a knowledge of chemistry is essential, but something more is also wanted, and that something is practice—practice in laboratory work-