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Twaddell's Hydrometer

This Hydrometer is much used in the bleaching and dyeing establishments in Scotland, and some parts of England. According to this scale O is equal to 1000, or the specific gravity of distilled water, and every additional 5 degrees of specific gravity adds 1 degree to Twaddell's scale. So that, in order to find the specific gravity corresponding to any degree of Twaddell's scale, multiply the degree by should be used for stirring, and the test liquid added drop by drop. 72. To find the strength of Acetic Acid by its Saturating Power. Dissolve 196+ grains pure crystallized bicarbonate of potassa in a little water; add to the solution sufficient water to make up exactly 1000 minims, or the 100 divisions of an acidimeter, a graduated glass tube of 100 divisions , each , division representing 10 minims. (See illustrations, No. 82.) A solution is thus formed, which, when added by degrees to 100 minims of the acetic acid or vinegar under examination, until the latter is exactly saturated, indicates the exact amount of acid present in the sample. Each minim of the alkaline solu- 5 and add 1000; thus, if this hydrometer tion thus employed represents 1 per cent. of shows 30°, 30 multiplied by 5 gives 150, and dry acetic acid. The test liquid must be added 1000 added makes 1150, the specific gravity. a drop at a time to avoid the risk of loss by To find the degree of Twaddell corresponding excessive effervescence. to any specific gravity, deduct 1000 from the 73. To find the strength of strong specific gravity, and divide the remainder by 5; the quotient will be the corresponding degree of Twaddell. Acetic Acid. If strong acetic acid be under inspection, it will be found convenient , previously to testing it, to dilute it with from 2 Thus, if it be required to find the degree of to 8 times its weight of distilled water, ac- Twaddell corresponding to 1150 specific grav- cording to its degree of concentration. Dilute ity, deduct 1000 from 1150, and divide the acid and vinegar require no further dilution. Instead of 1961 grains crystallized bicaracid and vinegar require no further dilution. Instead of 1964 grains crystallized bicarremainder, 150, by 5, and the quotient, 30, gives the degrees of Twaddell required. In this bonate of potassa, may be used either 135 way the corresponding degrees of Twaddell grains dry (see No. 12) carbonate of potassa, and Baumé can easily be found. Thus, 31 281 grains crystallized carbonate of soda, or degrees of Baumé are equivalent to a specific 104 grains dry carbonate of soda. (See No. gravity of 1275; and this, according to the above rule, will give 55 degrees Twaddell.

By reversing this process, Twaddell can as readily be reduced to Baumé. ng 80.) By using 981 grains (half the quantity) of the bicarbonate of potassa, we obtain a still more delicate test liquid; as each minim used for saturating a sample of acid will represent only 1/2 of 1 per cent. of dry acid. 74. To find the strength of Acetic cetimetry. The art of deter- Acid by Saturation without an Acidivinegar. Several methods are employed for applied to test by weight, instead of by an the purpose, based on-the quantity of acid acidimeter; 1000 grains of the test liquid are required for saturation; -the specific gravused in testing 100 grains of acid. Every ity after the liquid has been neutralized with grain of the test liquid necessary to produce hydrate of lime; - and the simple specific gravity. In all these methods, account should be taken of any mineral acid which may have been added, as is common with vinegars, to impart artificial strength. saturation indicates to grain of dry acid, and every ten grains are equal to 1 per cent.

Schuster's alkalimeter is a convenient instrument for this process. (See No. 82.) 1000 grains of the test liquid are introduced into the alkalimeter, and the whole weighed; the weight of the bottle and solution, after using such portion of its contents as is required for testing, deducted from the previous weight of that 51 parts of dry acetic acid are equal to of the solution consumed; this, divided by 10, 60 parts of glacial. (See No. 81.) Hence the gives the percentage of acid in the sample weight of glacial acid multiplied by .8512, tested. This method admits of great accuracy. 75. Practical test of the strength of gives the weight of dry acid; and the weight of dry acid, multiplied by 1.1748 gives a very Acetic Acid. A less accurate, but more close approximation to the weight of glacial convenient method for practical purposes, is as follows:-To 100 or 1000 parts (or grains) 70. To find the Comparative Weights of Dry and Glacial Acetic Acid. As both dry and glacial (or hydrated) acetic acid are referred to in many places, in speaking of strengths, it may be convenient to know the whole, gives the exact quantity in grains acid.