An inspection of these results shows that while the absorption goes on continually until it attains a maximum yet the amount absorbed in unit of time seems to vary with the temperature and pressure and it is probable that if these remain constant we shall obtain a more nearly uniformly decreasing rate. In his "Examination of Substances by the Time Method," Hannay has observed the rate at which the moisture was given off when Ca Cl, 6 H, O was dried in air at 100°, and, on comparing his Curve VI opposite page 3853, we shall note a singular resemblance to the curve given here notwithstanding that the observations were made from quite opposite standpoints.

It is to be regretted that the maximum increase of weight in my experiments should have been attained as the temperature fell and the barometer rose markedly, for these conditions might give rise to a deposition of moisture from the atmosphere in the bell glass which was presumably saturated. However, no bedewing was observed even after close inspection of the bell and watch glasses, yet this opinion is strengthened by the fact that while during the subsequent four days the temperature remained nearly constant at 16°, yet the average weight for I was 1.6968 and for II 2.3922 grams. After this the weighings were continued for some time but they fluctuated apparently, though not always, with the temperature, until when the temperature rose to 28°.5 the weights were 1.6573 grams for I, and 2.3397 grams for II. This variation in the power of bodies to attract or hold water at moderate temperatures, owing to a change of temperatures has been pointed out in the case of lime and ethyl alcohol by Squibb4, and Roscoe5 found in studying the hydrates of the volatile acids that under given circumstances of temperature and pressure there is for each acid a certain proportion of water which forms a stable compound, a weaker acid under that temperature and pressure giving off water, and a stronger acid giving off acid until the most stable compound remains behind.

In order to determine whether moisture was deposited on the vessel, an empty watch glass, nearly similar in form and size to those used, was placed beside them under the bell and weighed with the results shown in Table II.

3"Jour. Chem. Soc.," XXXII, 1877.

Squibbs Ephemeris, II, 533, 1884.

5 Quar. Jour. Chem. Soc. XIII, 146.

Although there was no such marked difference in temperature and pressure as occurred during March 29 to 31, yet during May 27 to 31 there was a similar change. These results show also the uniformity in the action of the balance at all the observed temperatures.

Let us now take the weights obtained from April 1 to April 4 as representing the maximum increase of weight at 16° and we have the following

Wt. CaCl2 in

Substance taken.

Wt. gained for

100 parts of
CaCl2

Molecules of H2O
attracted by
one molecule

of CaCl2.

Brandes found that 100 parts of his salt attracted 124 parts of water, after an exposure of 96 days, and from this we find that one molecule of the salt attracted 7.64 molecules of water. Hence my result is about seven times greater than that obtained by Brandes. The attraction too is found to be greater than that existing in the cryohydrate discovered by Guthrie.

The observations here recorded are only preliminary and it is recognized that the method employed is subject to several sources of error. To correct these it is proposed to arrange the experiments so as to maintain a nearly constant temperature. As the time required in the method used is very long it is proposed to shorten it by adding to the weighed portion of the anhydrous salt a determined quantity of water, but less than the amount which the salt would attract at the temperature of the experiment, and then to determine the rate of absorption from that point to the point of complete saturation. We may at least by this means determine the total attracting power at a given temperature with celerity and precision.

It is proposed too to use a vessel having the form of a right cylinder and of a sufficiently large diameter to render the effect of capillarity very slight, for as the absorption takes place from the surface, this is the only form of vessel in which the area of exposed surface will remain constant with a change in the volume of the liquid.

Finally it is proposed to use a substance which is deliquescent but which can withstand a high temperature for a considerable time without undergoing any other change in its constitution than loss of water, for in no other way can we have satisfactory evidence of complete dehydration.

AN EXPLANATION OF GLADSTONE AND TRIBE'S "2-3 LAW IN CHEMICAL DYNAMICS." By Prof. JOHN W. LANGLEY, University of Michigan, Ann Arbor, Mich.

IN the proceedings of the Royal Society Vol. XIX, page 498, and also in the Quarterly Journal of the Chemical Society, Vol. 9, will be found a paper by Messrs. Gladstone and Tribe entitled "A Law in Chemical Dynamics." The authors show, by a record of ex

periments, that if a plate of metal is suspended in a solution of another metal which it can precipitate (the plate being hung so that it reaches neither to the top nor the bottom of the liquid), the rate of chemical action shown by the loss of weight in the suspended plate, for a given period of immersion, will vary with

ROTATION, BRUSH AND CENTRIFUGAL EXPERIMENTS.

The numbers given are for 1 cm.2 of acting surface and for 1 minute of time, in fractions of a milligramme.

the percentage strength of the solution of the salt in a remarkable manner; which they epitomize in the statement, that if the percentages of salt be expressed by a series of the powers of 2, the chemical action will be expressed by the corresponding powers of 3, so that for percentages represented by 1, 2, 4, 8, etc., the rate

of action will be 1, 3, 9, 27, etc. They further state that this law of action holds good up to about three per cent., and that for solutions weaker than this, they have demonstrated it through a range of from 1 to 1,000,000.

They also give for the law a mathematical expression which seems to have been defectively printed, for when the typographical errors are corrected I find it to be expressed by

3
log. C=log. p. Xlog. K

where C is the rate of chemical action, p is the proportionate quantity of salt, and K is a constant. In the particular example given in their article they employed a plate of copper suspended in a solution of argentic nitrate. But the authors do not give any explanation of the law which they have discovered.

The following question at once arises, Is the rate of metallic precipitation for varying strengths of the solution due to the action of chemism alone, or, is the operation of chemical affinity compounded with one or more purely physical forces? and if so, what is the relative part contributed by each?

Messrs.Gladstone and Tribe point out that there are two currents, or mass movements produced. One, a light blue ascending stream of a dilute solution of silver and copper nitrates; the other, a deep blue descending current of copper nitrate containing about three times as much NO, as the main solution. Obviously the first step in an investigation of their results should be to bring the fluid against the plate with a uniform velocity. To accomplish this a piece of copper was slightly curved and fastened to an arm which carried it around in a horizontal circle of about one inch radius with a uniform speed of five and a half revolutions per second, which gave therefore a linear velocity of the metal through the liquid of nearly three feet per second. The strip was suspended from the arm so as to hang vertically, and the area of its surface was known. The results are given in the appended table in the columns marked 2 and 3. It was at once apparent that the absolute rate of action was much greater than when the metal was stationary, as in Messrs. Gladstone and Tribe's method where the only mass motion of the liquid relatively to the plate was caused by gravitation. An inspection of columns 2 and 6, where their method was followed, will show this.

In column 3 are given the quotients of the actual weights divided by the percentages of silver nitrate. It is apparent that these