The tricuspid is evidently abnormally large in relation to the mitral orifice.

If we suppose the other three orifices to be nearly normal (and it is evident that the pulmonic and aortic bear their normal relation to one another), we can calculate the excess of dilatation exhibited by the tricuspid opening

Hence the tricuspid is 58 inch in excess of its normal area, or more than one-third of its proper size in excess.

5. Bronchitis (Dr. Peacock).

The heart in this case weighed eleven ounces. As this does not much exceed its usual weight, it is clear that the pulmonic obstruction was slight. We should therefore expect to find but little deviation from the "law of the orifices."

Difference of the ratios = .01

This result fully bears out the inferences above made.

II. "On the Estimation of Ammonia in Atmospheric Air." By HORACE T. BROWN, Esq. Communicated by Dr. FRANKLAND. Received February 19, 1870.

In the attempts that have been hitherto made to estimate the ammonia present in atmospheric air, the results arrived at by the various experimenters have differed so widely that it is still a matter of uncertainty what the quantity really is. That it is a very small amount all agree, but the extreme results on record vary as much as from 13·5 to 01 part of carbonate of ammonium per 100,000 of air. It may therefore not be without interest to give an account of a simple method affording very concordant and, I believe, accurate results, at the same time being easy of performance and requiring but little time for an experiment.

The apparatus used consists of two glass tubes, each of about 1 metre

in length and 12 millims. bore. These are connected air-tight by means of a smaller glass tube, and inclined at an angle of 5° or 6° with the horizon. Into each of the larger tubes are introduced 100 cub. centims. of a mixture of perfectly pure water and two drops of dilute sulphuric acid. (sp. gr. 1.18). Through this acidulated water a measured quantity of the air under examination is slowly drawn, in small bubbles, by means of an aspirator.

No porous substance must be used to filter the air, for reasons to be stated hereafter. The air is conducted into the absorption liquid through a small piece of quill tubing drawn out to a small aperture at the end immersed. This tube must be kept quite dry throughout the experiment. Great care must be taken to cleanse perfectly every part of the apparatus with water free from ammonia, and the caoutchouc plugs, or corks, used must be boiled for a short time in a dilute solution of caustic soda.

The stream of air is so regulated as to allow about 1 litre to pass through the apparatus in an hour.

By directing the point of the delivery-tube laterally, each bubble has imparted to it on rising an oscillatory movement which facilitates complete absorption of the ammonia.

When from 10 to 20 litres of air have passed, the liquid is emptied from the tubes into upright glass cylinders, an excess of a perfectly pure solution of potash added, and then 3 cub. centims. of a Nessler solution. The standard of comparison is made in the ordinary way, only using acidulated in place of pure water, and neutralizing with potash after adding the standard solution of ammonium salt. Beyond somewhat retarding the point of maximum coloration, a little potassium sulphate does not interfere with the delicacy of Nessler's reaction.

If the experiment has been conducted with proper care, at least of the ɔtal ammonia ought to be found in the first tube. Four or five litres of air are generally quite sufficient to give a decided reaction, but it is better to use not less than 10 litres, as before mentioned*.

Very many experiments have been made by this method, both on air from the town of Burton-on-Trent, and that of the adjoining country. The air from the town, as might be expected, varies somewhat in composition; much more so than that taken from the open country, as may be seen from the following Tables, in which are given some of the numerous results obtained.

The ammonia is calculated in every case as carbonate ((NH), CO,); for although nitric acid is sometimes found in air, yet its presence must be looked upon as accidental.

* When the air to be examined is highly charged with ammonia, as that from stables &c., a perfectly dry bottle of 3 or 4 litres capacity should be carefully filled with a pair of bellows, 100 cub. centims. of acidulated water introduced, and, after closing securely, the whole well agitated at intervals for three or four hours. The liquid is then poured out, and the NII, estimated by the Nessler solution as usual.

In the immediate vicinity of towns some of the animonia must also be in the form of sulphate, sulphite, or ammonium chloride.

(1) Air taken from town. (Taken at a height of 2 metres from ground.)

(2) Air from country. (Taken at a height of 2 metres.)

The direction of the wind does not seem to have any influence on the ammonia found; immediately after heavy rain, however, the quantity falls somewhat below the average, but the air is again restored to its normal condition after a lapse of two or three hours.

Attempts were made to make the method more delicate still by absorbing the ammonia in pure water and then distilling, but the nitrogenous organic matter suspended in the air was found to interfere with the results.

When the air is passed through cotton-wool before entering the absorption-tubes, it is found to be entirely deprived of its ammonia by the filter. This is also the case with air artificially charged with ammonia to a large extent. This absorption is not due to the presence of hygroscopic moisture, since cotton-wool, when absolutely dry, is capable of taking up 115 times its own bulk of dry ammonia (confined over mercury) at 10°5 C. and 755.7 millims. barom., the gas being again slowly evolved when the wool is left in contact with the air at 100° C.

All other porous substances that were tried for filtering agents were found to possess this property more or less; even freshly ignited pumicestone is not entirely without absorptive effect upon the gas.

March 24, 1870.

Lieut.-General Sir EDWARD SABINE, K.C.B., President, in the Chair.

The following communication was read :—

"On the Madreporaria dredged up in the Expedition of H.M.S. 'Porcupine.'" By P. MARTIN DUNCAN, M.B. Lond., F.R.S., Sec. Geol. Soc., Professor of Geology in King's College, London. Received February 26, 1870.

Professor Wyville Thomson, Dr. Carpenter, and Mr. Gwyn Jeffreys have placed the collection of stony corals dredged up by them in the Porcupine' Expedition in my hands for determination. They have kindly afforded me all the information I required concerning the localities, depths, and temperatures in which the specimens were found.

My report has been rendered rather more elaborate than I had intended, in consequence of the great consideration of Professor A. Agassiz and Count de Pourtales in forwarding me their reports* and specimens relating to the deep sea-dredging off Florida and the Havana.

They have enabled me to offer a comparison between the British and American species, which I had not hoped to do before the publication of this communication.

CONTENTS.

I. List of the species, localities, depths, temperatures.

II. Critical notice of the species.

III. Special and general conclusions.

I. Twelve species of Madreporaria were dredged up, and the majority came from midway between Cape Wrath and the Faroe Islands. Others were also found off the west coast of Ireland. Many varieties of the species were also obtained, and some forms which hitherto have been considered specifically distinct from others, but which now cease to be sot. [See Table, p. 290.]

List of species known only on the area dredged, or in the neighbouring seas.

* Contributions to the Fauna of the Gulf-stream at great depths, by L. F. de Pourtales, 1st & 2nd series, 1868. Bull. Mus. Comp. Zool. Harvard College, Cambridge, Mass., Nos. 6 & 7.

+ One specimen came from the 'Lightning' Expedition. It must be remembered that all th deep-sea corals known to British naturalists were not dredged up. The Stylaster rosea, for instance, was not amongst the collection.

VOL. XVIII.

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