The specific gravity of a liquid is found by weighing it in a sp. gr. bottle, glass flask, or other vessel of known capacity, and dividing that weight by the weight of the same bulk of water; the quotient is, as before, the specific gravity. A bottle of the capacity of 1000 water-grains (specific gravity bottle) gives the density of a liquid at once, by simply filling it to the given mark, and then accurately weighing it.
We reprint from the ‘Journal of the Chemical Society’[179] a new method of determining the specific gravity of liquids, which is said by Dr H. Sprengel, the chemist who devised it, to be both expeditious and accurate. Dr Sprengel says:
[179] (2) xi, 577.
Fig. 1.
“The form of my instrument, as shown in the accompanying fig. 1, is that of an elongated U-tube, the open ends of which terminate
in two capillary tubes, which are bent at right angles in opposite directions. The size and weight of this instrument should be adapted to the size and capability of the balance in which it is to be weighed. As our usual balances indicate 1⁄10 milligram when loaded with 50 grams, the U-tube, when charged with the liquid, should not be heavier than 1000 gr. = (64·799 grams).
The instrument which served for my determinations, mentioned below, had a length of 17·7 cm. (7 inches), and was made of a glass tube, the outer diameter of which was 11 mm. (7⁄16 of an inch). It need hardly be mentioned that the U-shape is adopted for the sake of presenting a large surface, and so rendering the instrument sensitive to changes of temperature. The point, however, I wish to notice more particularly (for reasons explained below) is the different calibre of the two capillary tubes. The shorter one is a good deal narrower (at least towards the end) than the longer one, the inner diameter of which is about 1⁄2 mm. The horizontal part of this wider tube is marked near the bend with a delicate line (b). This line, and the extremity of the opposite capillary tube (a), are the marks which limit the volume of the liquid to be laid.
The filling of the instrument is easily effected by suction, provided that the little bulb apparatus (as represented in fig. 2) has previously been attached to the narrow capillary tube by means of a perforated stopper, i. e. a bit of an india-rubber tube tightly fitting the conical tubules of the bulb. On dipping the wider and longer capillary tube into a liquid, suction applied to the open end of the india-rubber tube will produce a partial vacuum in the apparatus, causing the liquid to enter the U-tube. As the partial vacuum maintains itself for some time (on account of the bulb, which acts as an air-chamber), it is not necessary to continue the suction if the end of the india-rubber tube be timely closed by compression between the fingers. When bulb and U-tube have about equal capacity, it is hardly necessary during the filling to repeat the exhaustion more than once.
Without such a bulb the filling of the U-tube through these fine capillary tubes is found somewhat tiresome; the emptying the U-tube is effected by reversing the action, and so compressing the air. After the U-tube has been filled, it is detached from the bulb, placed in water of the standard temperature almost up to the bends of the capillary tubes, left there until it has assumed this temperature, and after a careful adjustment of the volume, is taken out, dried, and weighed.