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III. "Description of an Improved Mercurial Barometer." By JAMES HICKS, Esq. Communicated by J. P. GASSIOT, F.R.S. Received March 16, 1864.

Having shown this instrument to Mr. Gassiot, he wished me to write a short description of it, which he thought would be of interest to the Royal Society.

Some time since I constructed an open-scale barometer, with a column of mercury placed in a glass tube hermetically sealed at the top, and perfectly open at the bottom. The lower half of the tube is of larger bore than that of the upper.

If a column of mercury, of exactly the length which the atmosphere is able at the time to support, were placed in a tube of glass hermetically sealed at the top, of equal bore from end to end, the mercury would be held in suspension; but immediately the pressure of the atmosphere increased, the mercury would rise towards the top of the tube, and remain there till, on the pressure decreasing, it would fall towards the bottom, and that portion which the atmosphere was unable to support would drop out. But if the lower half of the tube be made a little larger in the bore than the upper, when the column falls, the upper portion passes out of the smaller part of the tube into the larger, and owing to the greater capacity *of the latter, the lower end of the column of mercury does not sink to the same extent as the upper end, and the column thus becomes shorter. The fall will continue until the column is reduced to that length which the atmosphere is capable of supporting, and the scale attached thus registers what is ordinarily termed the height of the barometer.

From the above description it will be evident that, by merely varying the proportion in the size of the two parts of the tube, a scale of any length can be obtained. For example, if the tubes are very nearly the same size in bore, the column has to pass through a great distance before the necessary compensation takes place, and we obtain a very long scale, say 10 inches, for every 1-inch rise and fall in the ordinary barometer. But if the lower tube is made much larger than the upper, the mercury passing into it quickly compensates, and we obtain a small scale, say from 2 to 3 inches, for every inch. To ascertain how many inches this would rise and fall for an ordinary inch of the barometer, I attach it, in connexion with a standard barometer, to an air-pump receiver, and by reducing the pressure in the air-pump I cause the standard barometer to fall, say 1 inch, when the other will fall, say 5 inches; and so I ascertain the scale for every inch, from 31 to 27 inches.

It was on this principle that I constructed the open-scale barometer, which has since been extensively used. But having been asked to apply a vernier to one of these barometers graduated in this way, I found this impracticable, as each varied in length in proportion as the bore of the tube varied, so that every inch was of a different length.

VOL. XIII.

I have now remedied this defect, and made what I believe is an absolute standard barometer, by graduating the scale from the centre, and reading it off with two verniers to the Tth of an inch. The scale is divided from the centre, up and down, into inches, and subdivided into 20ths.

To ascertain the height of the barometer graduated in this way, take a | reading of the upper surface of the column of mercury with the vernier, then of the lower surface in the same way, and the two readings added together will give the exact length of the column of mercury supported in the air, which is the height of the barometer at the time.

There is another advantage in this manner of graduating over the former, that if a little of the mercury drops out it will give no error, as the column will immediately rise out of the larger tube into the smaller, and become the same length as before; but by the former scale the barometer would stand too high, until readjusted, which could only be effected by putting the same quantity of mercury in again.

I have introduced Gay-Lussac's pipette into the centre of the tube, to prevent the possibility of any air passing up into the top.

The Society then adjourned over the Easter Recess to Thursday, April 7th.

"On Mauve or Aniline-Purple." By W. H. PERKIN, F.C.S. Communicated by Dr. STENHOUSE. Received August 19, 1863*.

The discovery of this colouring matter in 1856, and its introduction as a commercial article, has originated that remarkable series of compounds known as coal-tar colours, which have now become so numerous, and in consequence of their adaptibility to the arts and manufactures are of such great and increasing importance. The chemistry of mauve may appear to have been rather neglected, its composition not having been established, although it has formed the subject of several papers by continental chemists. Its chemical nature also has not been generally known; and to this fact many of the discrepancies in the results of the different experimentalists who have worked on this subject are to be attributed.

The first analysis I made of this colouring matter was in 1856, soon after I had become its fortunate discoverer. The product I examined was purified as thoroughly as my knowledge of its properties then enabled me, and the results obtained agree very closely with those required for the formula I now propose. Since that time I have often commenced the study of this body in a scientific point of view, but other duties have prevented me

*For abstract see vol. xii. p. 713.

The substance I examined was doubtless the sulphate, of which I made two combustions:

No. I. gave 71.55 per cent. of carbon and 6.09 per cent. of hydrogen.

No. II. gave 71.60

Theory requires 71.5

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from completing these investigations; but, although unacquainted with its correct formula, its chemical characters have necessarily been well known to me for a considerable time. When first introduced, commercial mauve appeared as an almost perfectly amorphous body; but now, owing to the great improvements which have been made in its purification, it is sent into the market perfectly pure and crystallized.

On adding a solution of hydrate of potassium to a boiling solution of commercial crystallized mauve, it immediately changes in colour from purple to a blue violet, and after a few moments begins to deposit a crystalline body. After standing a few hours, this crystalline product is collected on a filter, washed with alcohol once or twice, and then thoroughly with water. When dry, it appears as a nearly black glistening substance, not unlike pulverized specular iron ore.

This substance, for which I propose the name Mauveine, is a powerful base. It dissolves in alcohol, forming a blue violet solution, which immediately assumes a purple colour on the addition of acids. It is insoluble, or nearly so, in ether and benzole. It is a very stable body, and decomposes ammoniacal compounds readily. When heated strongly it decomposes, yielding a basic oil, which does not appear to be aniline.

The following analyses were made of specimens dried at 150° C. :

I. 301 grm. of substance gave 8818 of carbonic acid and ⚫162 of water. II. 2815 grm. of substance gave 8260 of carbonic acid and 145 of water.

Direct Nitrogen determination.

III. 3435 grm. of substance gave 410 c. c. N at 23°C. and 766 mms. Bar. 41.0 cub. centims. (766·0 millims.-20.9)

V'

824.1 millims.

=37.7 cub. centims.

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*

The formula, C, H, N., requires the following values:

III.

13.75

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Hydrochlorate of Mauveine.--This salt is prepared by the direct combination of mauveine and hydrochloric acid. From its boiling alcoholic solution it is deposited in small prisms, sometimes arranged in tufts, possessing

* C=12.

a brilliant green metallic lustre. It is moderately soluble in alcohol, but nearly insoluble in ether. It is also, comparatively speaking, moderately soluble in water.

162 of water.

163 of water.

100° C. gave the following numbers :-
8255 of carbonic acid and
8275 of carbonic acid and
8345 of carbonic acid.
851 of carb. acid and
6603 of carb. acid and
205 of chloride of silver.
195 of chloride of silver.

Different preparations dried at
I. 306 grm. of substance gave
II. 308 grm. of substance gave
III. 310 grm. of substance gave
IV. 3165 grm. of substance gave
V. 2447 grm. of substance gave
VI. 627 grm. of substance gave
VII. 560 grm. of substance gave

16525 of water. 1356 of water.

VIII. 69 grm. of substance gave 2266 of chloride of silver.

Direct Nitrogen determination.

IX. 3497 grm. of substance gave 40 c. c. N at 20°C. and 777.2 mms. Bar. 40 c. c. (7772-17.4)

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=37.2 c. c. at 0° C. and 760 millims. Bar.

815.8 millims.
37.2 cub. centims. × 0012562 grm. 04673 grm. N.

These numbers correspond to the following percentages:—

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These numbers agree with the formula C2, H2, NH Cl,

27 24

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Mean of experiment.

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I have endeavoured to obtain a second hydrochlorate containing more acid, but up to the present time have not succeeded. Platinum-salt.-Mauveine forms a perfectly definite and beautifully crystalline compound with bichloride of platinum. It is obtained by mixing an alcoholic solution of the above hydrochlorate with an excess of an

alcoholic solution of bichloride of platinum; from this mixture the new salt separates as a highly crystalline powder. I have generally preferred to use cold solutions in its preparation; but if moderately hot solutions be employed, the salt will separate as crystals of considerable dimensions.

This platinum-salt possesses the green lustre of the hydrochlorate, but, on being dried, assumes a more golden colour. It is very sparingly soluble in alcohol. The following numbers were obtained from various preparations dried at 100° C. :

I. 44125 grm. of substance gave '072 of platinum.

II. 4845 grm. of substance gave '079
III. 511 grm. of substance gave ⚫083
IV. 510 grm. of substance gave ⚫083
V. 6345 grm. of substance gave ⚫1035
VI. 618 grm. of substance gave ⚫101

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VII. 31275 grm. of substance gave 60525 of carbonic acid and ⚫118 of water.

VIII. 30675 grm. of substance gave 595 of carb. acid and 110 of water. IX. 3795 grm. of substance gave 27 of chloride of silver.

These results correspond to the percentages in the following Table :

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The formula, C, HN, H Pt Cl,, requires the following values :

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Gold-salt. This compound is prepared in a similar manner to the platinum-salt, only substituting chloride of gold for chloride of platinum. It separates as a crystalline precipitate, which, when moist, presents a much less brilliant aspect than the platinum derivative; it is also more soluble than that salt, and when crystallized appears to lose a small quantity of gold. The following results were obtained from a specimen dried at 100° C. :

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