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. gained for 100 parts of Molecules of H2O 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. 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 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 numbers tend toward a constant, and, in this respect, they show a marked contrast to the numbers in column 7. The experiments were next varied by varnishing the copper on its convex side and holding it rigidly against the side of a beaker while its bare concave face was constantly swept by a rotating cylindrical brush, driven at uniform speed by clockwork. The results are given in columns 4 and 5, where, to secure a greater range for comparison, a different order of per cents was employed, and it is evident from column 5, that the absolute rate is less than for the rotation experiments, but is still much greater than for the gravitative record; also it is apparent that the quotients here also tend to approach a constant [.6]. The first two numbers in columns 3 and 5 depart widely from the others. This is due, I believe, to the necessity of removing the silver each time the copper was weighed to determine how much of it had been dissolved. When the solution is very weak, the silver crystals are so minute that it is practically impossible to remove them completely, while for larger crystals, made by stronger solutions, there is no such difficulty. Now when the extreme difficulties of securing absolutely uniform rotation, of detaching the copper at a given instant, and of preventing accidental cross currents are considered, these numbers show (since they are the means of many trials) that the chemical action varies directly with the quantity of salt in solution, when the supply of fresh liquid to the surface of the plate is constant and independent of its strength. Within the limits of these experiments, the following law would appear to be true. In metallic precipitations of dilute solutions, the chemical action varies directly as the mass, i.e., percentage, of the dissolved salt. The experimental work of Messrs. Gladstone and Tribe is above criticism. I made many determinations by their method, with the sole result of confirming their entire accuracy. How then can their law be reconciled with the above statement? The explanation I venture to offer is the following: When the plate is suspended in the liquid, a film of copper nitrate is at once formed against it. Now the access of fresh silver nitrate depends on the removal of copper nitrate; this film being heavier than the main solution begins to fall (a part also rises) and thus drags in fresh liquid from above to attack the copper. The rate at which it falls depends on its density, that is |