7. The result of two other experiments on oxalate of lime was very nearly the same as the preceding. The following may be stated in round numbers as the mean of the whole. Oxalic acid is a compound of

8. The only other analysis of oxalic acid with which I am acquainted has been given by M. Fourcroy, as the result of his own experiments, in conjunction with those of Vauquelin*. It is as follows:

Systeme de Connois. Chem. vii. 224.

It gave me considerable uneasiness to observe, that my experiments led to conclusions irreconcileable with those of chemists of such eminence and consummate skill, and it was not without considerable hesitation that I ventured to place any reliance upon them. I am persuaded, however, that some mistake has inadvertently insinuated itself into their calculations; since the carbonic acid alone, formed during the distillation of oxalate of lime, contains considerably more carbon than the whole quantity which they assign to the oxalic acid decomposed. M. Fourcroy informs us, that oxalic acid is converted into carbonic acid and water, when acted upon by hot nitric acid; and this decomposition seems to have been the method employed to ascertain the proportion of the constituents of oxalic acid; but the numbers assigned by him do not correspond with this statement. For 10 parts of hydrogen require 60 of oxygen to convert them into water, and 13 of carbon require at least 33 of oxygen. So that instead of 77 parts of oxygen, there would have been required no less than 98 to convert the hydrogen and carbon into water and carbonic acid. It is true, that the surplus of oxygen may be conceived to be furnished by the nitric acid; but if this be admitted (and I have no doubt from experience that the nitric acid actually does communicate oxygen), it is difficult to see how the constituents of oxalic acid could be determined by any such decomposition, unless the quantity of oxygen furnished by the nitric acid were accurately ascertained.

[To be continued.]

XLVII. De

XLVII. Description of Mr. G. ATKINS'S Hydrometer for determining the Specific Gravity of both Solids and Liquids.

SIR,

To Mr. Tilloch.

THE present improved state of chemistry; its application to so many of our principal manufactures, and the necessity of determining the specific gravity of the various substances which are used in them, or affording in all cases an important indication with regard to their qualities, and being in many the only accurate measure of their value, may perhaps render the following description of an instrument for this purpose not unacceptable to your numerous readers. By giving it a place in your valuable Magazine you will therefore oblige, Sir, your obedient servant,

57, Dorset-Street, Fleet-Street, Sept. 10, 1808.

GEO. ATKINS.

The specific gravity, or comparative weight of the majority of those substances which fall under the observation of the manufacturer, the mineralogist, or the chemist, having always been considered as one of their most distinguishing characteristics, a variety of methods have at different periods been resorted to for ascertaining it.

In point of accuracy, perhaps, the best mode of taking the specific gravity of a body is by a very good hydrostatic balance. This instrument, however, we may venture to affirm, can scarcely ever be obtained sufficiently perfect to be depended on for so nice a purpose.

Persons who are in the habit of adjusting balances, and those who use them with considerable care, well know the various sources of error to which they are liable. The circumstance of the arms of a beam being in equilibrio, is no proof of its correctness, unless it will remain so when either loaded or unloaded, and with exchange of scale-pans. The necessity of having a piece of steel for the beam which shall be perfectly homogeneous; the uncertainty with regard to the exact equality of the arms, in both weight and length; and, even when very nicely adjusted, its liability to acquire

polarity,

polarity, and consequent derangement by magnetism; the expansion of either arm by the heat of the hand, or its contraction by a current of air, renders those instruments extremely liable to give anomalous results.

But supposing the balance not liable to error, it is too complicated in its use for any other than the man of science, in his closet, where time and close attention may be afforded; and since the application of science to the arts has become so general, chemists, manufacturers of acids, brewers, dyers, distillers, and all others whose manufacture consists of any chemical process, require a more simple and expeditious mode of ascertaining the specific gravity, and consequently the value of their articles, than by the hydrostatic balance. Indeed, in many concerns its use would be impracticable, it being necessary to intrust the business of examining the qualities of the substances in question to persons who have neither time or knowledge sufficient to enable them to apply an instrument of such a kind.

The HYDROMETER, on a variety of constructions, has been long made use of by distillers and all dealers in spirituousliquors; and of late years brewers have generally adopted it, for its simplicity and facility in use compared with the hydrostatic balance or weighing bottle. But as the hydrometer for spirituous-liquors, and the saccharometer for maltliquors, (which the author of this paper is in the habit of manufacturing,) are adapted solely to their respective purposes, he has long thought it a very desirable object to construct an instrument which would combine simplicity with an universality of application to all substances, fluid and solid, of which it might be requisite to ascertain the specific gravity. And it is presumed that this object is accomplished in the instrument about to be described.

Among the principal subjects of consideration in the construction of hydrometers, are, the form of the instru ment which shall be best adapted to facilitate its motion in a fluid, and that it be of a convenient size, both for the sake of portability, and that it may require as small a sample of a fluid as possible to make an experiment with.

With these views, the spheroidical form is that which

has

has been preferred for the bulb of this instrument, on account of its more readily dividing the fluid in its passage up and down; and the size of it is such, that half a pint of any liquid is sufficient for trial with it.

The hydrometer (see Plate IX.) consists of the bulb b, a small stem a c, with a cup d on its top to receive weights, and a shank ef beneath the bulb with a pointed screw, to which is affixed a cup g, to receive weights or solids when their specific gravities are required to be taken.

The instrument is accompanied with an accurate set of grain weights.

The weight of the hydrometer itself is 700 grains, and on adding 300 grains in the upper cup, and immersing it in distilled water, at the temperature of 60 degrees, Fahr. it will subside to the middle mark on the stem, and will then consequently displace 1000 grains of water.

It follows, therefore, from this adjustment of the bulk of the instrument, that each grain in the upper cup will represent one thousandth part of the specific gravity of the water, or one unit in specific gravity, if that of water be taken to be 1000; and one-tenth of a grain one-tenth of unit, which is also the value of each of the small divisions on the stem; and accordingly, when the hydrometer is immersed in any liquid until it sinks to the middle point on the stem, the specific gravity of such fluid will be indicated by the sum of the weight of the instrument (which is, as before stated, 700 grains) and the grains added in the upper

cup.

Suppose, for example, that, on immersing the instrument in ether, it requires 34 grains in the top cup to make it subside to the middle mark on the stem. The specific gravity of such ether will in this case be 700 + 34 = ·734. And on putting the instrument into alcohol or wort, if it requires in the former case 125 grains, and in the latter 355, the specific gravity of the spirit will be 825, and that of

the wort 1.055.

To ascertain the specific gravity of a solid, we have to take any fragment less than 300 grains; find its weight in air, and its weight in water, and take their difference; and on

dividing