the process of Fresenius } {81 ” ” (glacial). and Will). } {50 Succinic acid (dry or anhydrous crystals). 22 ” dry carbonic acid (when } {59 ” ” (ordinary crystals). a dry carbonate is } {40 Sulphuric acid (anhydrous). used). } {49 ” ” (liquid, _monohydrated_, sp. { gr. 1·8485). {75 Tartaric acid (crystallised). {212 Tannic acid (carefully dried). [Footnote 8: 1000 water-grains measure of pure liquor of ammonia, sp. gr. 0·992, contains exactly 17 gr., or 1 equiv. of pure gaseous ammonia. A standard liquor of this strength may be most conveniently prepared by cautious dilution of a stronger solution, until a hydrostatic bead, corresponding to the sp. gr., floats indifferently in the middle of the new solution, at 60° Fahr. By keeping two hydrostatic beads in the solution——the one made barely to float, and the other barely to sink——we shall always be able to detect any change of strength or temperature which it may suffer; since the “loss of a single hundredth part of a grain of ammonia per cent., or the difference of a single degree of heat, will cause the beads to” vary their positions. To preserve its integrity it must be kept in a well-stoppered bottle. (See below.)] [Footnote 9: These substances, as well as ‘test-solutions’ containing them, must be perfectly free from carbonic acid, and must be carefully preserved to prevent the absorption of carbonic acid from the atmosphere. Mohr states that a dilute solution of either of them is best preserved in a flask or bottle well closed with a cork fitted with a small bulb tube (resembling a chloride of calcium tube), filled with a finely triturated mixture of sulphate of soda and caustic lime, and bearing a very thin open tube in the exit aperture. Fresenius, and most other foreign chemists, prefer ‘test-solutions’ of pure soda. With test-solutions containing caustic alkalies, exact neutralisation of an acid is not only more easily effected, but more readily perceived, particularly when either solution is tinted with litmus.] [Footnote 10: Prepared by gradually heating the pure crystallised carbonate to redness. From being uniform in composition, and easily procured or prepared, they are much employed; preference being usually given to the soda-salt.] [Footnote 11: The crystals must be free from attached water, but not the least effloresced.]