[Microscopical and Natural History Section.]

Ordinary Meeting, December 16th, 1895.

JOHN BOYD, Esq., President of the Section, in the Chair. Mr. STIRRUP exhibited specimens of kelp from Tory and Arran Islands, off the West Coast of Ireland.

Mr. MELVILL read a paper on "The Distribution of Simethis bicolor (Kunth)," and exhibited specimens from Branksome, Dorset.

Ordinary Meeting, January 7th, 1896.

HENRY WILDE, F.R.S., President, in the Chair.

The thanks of the members were voted to the donors of the books upon the table.

Dr. C. H. LEES exhibited, on behalf of Dr. A. SCHUSTER, F.R.S., some photographs obtained by Professor Röntgen, of Würzburg, by means of radiations of an apparently new kind. These radiations are pro

duced in Crookes' Crookes' vacuum tubes, and pass readily through paper, wood, and flesh, less readily through glass, crystals, and thin films of metal, and are absorbed by thicker films of metal and by bone. As far as Röntgen's experiments go, these rays are neither reflected nor refracted, nor has a double refracting medium any apparent effect in polarising them.

Mr. J. C. MELVILL, M.A., F.L.S., read a paper entitled "Notes on the British Distribution of Simethis bicolor (Kunth)," a wild member of the lily tribe only found in the neighbourhood of Bournemouth and in one station in Ireland, as regards the United Kingdom, though having a wide range through Western Europe. Mr. Melvill's opinion is, however, that it is, nevertheless, indigenous to the British Isles.

Some Experiments on the Latent Heat of Steam. By J. A. Harker, D.Sc., Berkeley Fellow in Physics in the Owens College, Manchester.

by Dr. Schuster, F.R.S.

Communicated

(Received January 23rd, 1896.)

Fourth

In a communication made some time ago to the Literary and Philosophical Society of Manchester (Memoirs and Proceedings, Eighth Series, Vol. ., pp. 37-53), Mr. P. J. Hartog and the author described some preliminary experiments on the latent heat of steam made with a modified form of the apparatus designed for the purpose by M. Berthelot (Mécanique Chimique, Vol. I., p. 288). The original object of the work was more to test the accuracy of the results given by a small apparatus of this kind than a redetermination or even control of the work of previous observers.

A somewhat long series of experiments with variations in many of the details-for example, the different means of protecting from radiation the vertical tube down which the steam passes to the calorimeter-led to the surprising result that the value of L, the latent heat of condensation of steam at 100°, came nearly 2 per cent. lower than that found by Regnault in his classic researches, an account of which was published in the Mémoires de l'Académie des Sciences in 1847.

On looking up the literature of the subject we found that, except the experiments of Berthelot, which were discussed in the paper alluded to, no results had been published which could at all be regarded as a confirmation

of Regnault's work. I therefore resolved to try and ascertain the cause of the discrepancy we had observed, and with this intention resumed the work last year.

The results given by the five preliminary experiments quoted in the paper (loc. cit.)* agreed well among themselves, though the duration of the experiment, the total rise, &c., varied considerably. I thought it desirable, however, to see if a longer series of such experiments agreed equally well among themselves, and made altogether fifteen similar ones. Though most of these gave almost exactly the same value of L as the ones quoted, I was surprised to find one or two came out considerably higher, giving a value approximating to that of Regnault.

Considering the various sources of error in an experiment of this kind, one of the first things one might expect to be accountable for such differences is the thermometer used. All the experiments, including those to be described, were made with the same thermometer, one of French hard glass, by Baudin of Paris (No. 12,771), similar to, and made in the same batch as the one used in the calorimeter by Schuster and Gannon in their determination of the Mechanical Equivalent of Heat (Roy. Soc. Trans., 1895, Vol. 186). This thermometer had been most accurately calibrated and compared by them with a Tonnelot Standard, whose constants had been determined at the Bureau Internationale des Poids et Mesures at Sèvres. The scale of the thermometer I used extended from 0°-13°, Dr. Schuster's from 12°-25°, and by his kindness I was allowed to obtain by direct comparison the correction of my thermometer at 12°. Thus from determinations of the zero corresponding to this temperature, and a calibration of the stem from 0-12, made with various

*The highest value was 5259, the lowest 5236, or, excluding one experiment done under abnormal conditions, 524'1, the mean in that case being 524 8.

threads, one, two, three, and six degrees in length, I could obtain the value of the fundamental interval and the correction for each whole degree of the scale. Except the one for the fundamental interval, the corrections were found to be so small that even in the measurement of an interval, where the two corrections had to be added together, they were almost negligible.

The next question that might be raised is with regard to the dryness of the steam formed in the boiler, and its possible partial condensation on its way to the calorimeter.

In order to maintain regularity of boiling in the glass apparatus, in all the experiments a few pieces of crumpled platinum foil were put into the generator, and in no case was the flame allowed to impinge directly on to the glass, the whole of the glass surface being surrounded by a double layer of copper gauze. In order to test if liquid particles, formed by the bursting of steam bubbles on the surface of the water, could by any chance pass over into the calorimeter, the following test was devised:

The boiler was filled with a 5% solution of potassium permanganate, and the distillate examined calorimetrically in Nessler glasses. The experiment was repeated under varying conditions and with different rates of boiling, in some cases much faster than in any L determination, but in no case could any certain colouration be detected in the distillate, even though if one part in ten thousand had been carried over in the liquid form it could easily have been recognised.

The further question, as to whether the steam, even though dry on leaving the generator, might not on its way to the calorimeter lose some heat by radiation, and thus hold condensed water in suspension, was more difficult to decide. One obvious thing to be done was to make the path of the steam from the generator to the condenser as short as possible.

With the Berthelot apparatus and the modification of the same referred to above, the source of heat for the boiler must lie underneath it and directly above the calorimeter. Many different kinds of lids were used to protect the calorimeter from the heat radiated by this flame, but the total correction could seldom be reduced below 3% of the observed rise, and on this there remained. some little uncertainty.

A metal apparatus was now designed in which the heat was supplied by an electric current passing through a coil of wire immersed in the water of the generator. This is shown in Fig. 1. A cylinder of copper, A B, 8 cm. diam. and 20 cm. long, is provided above and below with brass plates, which screw up against leather washers, making a steam-tight joint. Through the lower plate is fixed, centrally, a vertical brass tube 6 mm. internal diam., which passes up the cylinder to just under the upper plate and downwards to the steam-trap D, consisting of a short piece of wider tubing having a screw plug at F.

From this trap the steam passes along the inclined tube to the three-way tap C, by which it can either be led away by the horizontal tube or downwards to the condenser. The whole of the tubes outside the boiler were wrapped with in. lead pipe, known in the trade. as "twigging," through which a current of steam from a second boiler could be passed. I found this a most effectual and convenient way of jacketing any pipes which had to be protected from radiation, and it was often used in these experiments.

The construction of the coil for supplying heat to the water in the boiler gave considerable trouble. Although a coil of bare wire could be wound on smooth supports so tight as to be perfectly satisfactory when used in cold water, yet at 100° it always became loose, and short