an upright condenser, precisely in the same manner as the first. In this second flask it is practically entirely decomposed. The C2H2 is then passed through alcohol at 0° (to absorb traces of CH,Br), then through two Wolf's bottles filled with water, and lastly through two CaCl, tubes. The gas may then be considered practically pure. To test this, I passed it for about half an hour through the two weighed flasks, surrounded by a mixture of ice and salt, but at the end of that time they had not gained in weight to speak of. To prepare first cuproso vinyl oxide

C.CHO (Berthelot.)

and then decompose this by dilute hydrochloric acid, is an extremely tedious and troublesome operation, and offers very little corresponding advantage. Sabanjeff discusses the other known methods for the preparation of CH, very fully in his paper. I also tried some of them, but found the above by far the best of all.

Action of Acetylene (C2H2) on ICl.

On passing CH, over pure dry ICl, at 0°, combination takes place with great evolution of heat. I always found more or less iodine separated out. My chief object being to try to prepare the compound, CH,CHI, I did not investigate farther the products formed. Probably, if the ICl, were kept cold in a mixture of ice and salt, and the CH, diluted with air and passed over it very slowly, one might get the compound C2H ̧Cl ̧L

Action of CH, on ICl.

(a.) On pure IC1 at 0°.

The evolution of heat produced by the combination was so great that more or less iodine always separated out.

(b.) On ICl dissolved in excess of ether at 0°.

The ether used must be perfectly free from alcohol and water. The C2H2 was passed as quickly as possible through this ethereal solution, to reduce as much as might be the secondary reaction of the ICI on the ether. It was absorbed greedily.

After saturation the ethereal solution was diluted with water, when a heavy liquid settled to the bottom. This was washed with dilute NaOH solution, and then with water, and dried over CaCl.

What ether remained in the above liquid was distilled off at 35° to 40° in a current of CH. Even at this temperature a slight decomposi tion occurred (iodine separating), so I stopped heating. It was found practicable, however, to fractionate the liquid (with very slight decomposition) in a current of steam. Repeated fractionating yielded

(1.) Ether+C2H,Cl,, &c. (not examined).

(2.) C2H2Cl+.

(3.) Solid C2H,I2.

To ascertain the composition of the above liquid I analysed it.

+0.6687 grm. ignited with pure CaO gave

(after converting AgI into AgCl by current of Cl).

The above figures do not agree very exactly, but I had too small a quantity of the compound to be able to fractionate it perfectly. It was found impossible to determine its boiling point, as it decomposed very rapidly on heating, with separation of iodine.*

Spec. Grav.

2.41 at 13.5° C.

Acetylene chlor-iodide is an ethereal liquid with much the same odour as the corresponding ethylene compound. Its vapour attacks the eyes. It does not decompose to any extent if kept in the dark.

Remarks on Acetylene Iodide (C2H2I2).

I prepared from 50 to 60 grms. of the above compound by passing the gas through a saturated alcoholic solution of iodine. As the two

* It seemed to boil at first, on heating very rapidly, between 180° and 190° C., but this is not reliable.

combine very slowly, the iodine must be distributed in numerous small flasks, which ought to be hung on a glass rod, horizontally placed, to admit of their being shaken from time to time. (See Sabanjeff, Annalen, Band 178; also Semenoff (for C2HI2), Zeitschrift für Chemie, 1864.)

Sabanjeff states that he, while preparing the iodide in this manner, got at the same time a large quantity of a liquid iodide (also of the formula C2H2I2). He supposes the one to

CHI

be || CHI

CH2

and the other ||
CL2

Curiously enough, I only obtained a

few drops of a liquid which could at all correspond to this second iodide. Whether it was the iodide, or a product of the action of the iodine in the alcohol, &c., I cannot say. The quantity got was too small.

The chief object which I had in view in preparing the preceding acetylene compounds (chlor-iodide, iodide, also tetrabromide, &c.), was that from them I might be able to obtain the corresponding cyanogen ones, which, if got and treated with an alkali, would probably have yielded chloro- (or iodo-) acrylic, and fumaric or maleic acids. I have not, however, as yet succeeded in obtaining them.

Whether C2H, combines with iodide of cyanogen when the latter is dissolved in alcohol, I cannot yet say. It does not with dry ICN.

All attempts to obtain the cyanogen compounds of C.H, by heating in sealed tubes (at temperatures ranging from 120° to 0°25) chlor-iodide or iodide of acetylene with the various cyanides {KCN, AgCN, (AgCN+KCN), H¿(CN2),} or with ICN and a metal, were fruitless.

When H2(CN)2 was used, generally no reaction occurred, and in nearly all the other cases ammonium salts were formed in large quantity. I had unfortunately only a small quantity of the chloriodide at my disposal.

Acetylene does not seem to be absorbed if passed into a hot solution of "nascent" formic acid, i.e., a solution containing KCN and KOH.

a

4. On some Definite Integrals. By Professor Tait.

The integrals referred to occur in connection with applications of
the Method of Electric Images. A curious special case was given
to the Society in July 1875, but was not inserted in the "Pro-
ceedings." It depended on the fact that the image of a sphere,
whose surface density is inversely as the cube of the distance from
a point, is another sphere with a similar law of distribution. But
any desired number of integrals, whose values can be at once
assigned, may be obtained by various applications of the following
process. Take any centrobaric distribution of electricity, and calcu-
late directly the density induced by it at any point of an uninsulated
sphere. This must be inversely as the cube of the distance from
the centre of gravity of the given distribution.

Take, as a simple example, a uniformly charged sphere of non-
conducting matter with unit charge, radius a, at a distance p from the
centre of an uninsulated sphere of radius r. Suppose r >a+p, so
that the inducing sphere is wholly internal.
above that the density of the induced charge at points defined by
radii making an angle a with the line of centres is represented by

We see by the method

[r2 + a2 + p2 − 2ap cos 0 - 2rp cos a+2ar (cos a cos - sin a sine cos 4)]{ ̄ ̄ (r2+p2 — 2rp cos a)}]

i.e., the double integral is independent of a.

Again, if the unit charge on the small sphere be distributed inversely as the cube of the distance from the centre of the large one, we have obviously for the induced density on the large sphere the expression

SS

(a2 — p2) (r2 — a2 — p2+2ap cos 0) sin Odedø

[a2+p2 - 2ap cos 0] [r2+a2+p2 - 2ap cos 0 − 2rp cos a+2ar (cos a cos-sin a sin cos 4).

But if the small sphere include the centre of the large one, i.e., if
a>p, the induced density is uniform; so that the value of the

If a<p, similar reasoning shows that the value is

These values agree, as they should do, when a=p.

Monday, 1st April 1878.

Sir WILLIAM THOMSON, President, in the Chair.

The following communications were read :—

Chapter IV.

By

1. Chapters on the Mineralogy of Scotland.
Augite, Hornblende, and Serpentineous Change.
Professor Heddle.

(Abstract.)

A couple of months ago I had the honour of submitting to the Society a speculation upon the metamorphism of a particular rock mass. To-night I again return to metamorphism, submitting, however, not a speculation, but the closely elaborated process of the change which has affected another rock.

It is perhaps natural that the attention of one who approaches geology from the chemical and mineralogical sides should be immediately directed to those rocks which are either aggregates of simple minerals, or which are the products of changes effected upon simple minerals; natural also that consideration should be first given to those in which that change has been more immediately chemical than physical.

To no rock mass does this apply more directly than to serpentine. In my wanderings I have visited and closely observed the relationship of-with a single exception-every bit of this rock which is to be found between Unst and Tyree on the one hand,-Harris and the Black Dog Rock on the other.

In my analyses of a number of ill-defined minerals, generally believed to be products of the alteration of augite and hornblende,