The relation between the quantity of electricity and the specific gravity of the sulphate of zinc.-Svanberg's experiments are quoted by recent writers to prove that the electro-motive force for Daniell's battery is not materially changed by the nature of the liquid about the zinc. Although this statement is strictly true, yet it does not give us correct views in regard to the battery. We prepared different solutions of s. z. ranging from zero to saturation. These were alternately used in the porous cell and q. measured by the galvanometer. The time for each experiment was about five minutes. Above the specific gravity of 15° B. q. was sensibly the same up to saturation. These results were so directly contrary to all our experience with the battery in actual use, that at first we were at a loss to understand them. The experiments were accordingly continued, by putting an element on a closed circuit through the galvanometer. The quantity of electricity and the specific gravity of the s. z. was then noted from time to time. So soon as the s. z. approached near saturation, from 43° to 46° B. depending on the temperature, it was found that the element gradually decreased in force until finally q. was less than one twentieth of its normal value. As the electro-motive force remained constant it indicated an internal resistance more than twenty times as great. But we know by direct experiment that a saturated solution of s. z. is a better conductor than a dilute solution, and hence we ought to expect the resistance to be less. A careful study of the phenomena led us to conclude that the increased resistance was due to the polarization in the battery itself. When the current is passed through a voltameter or electrolyte solution, it is found a much greater resistance is introduced, than that due to the liquid alone. This increased resistance is ascribed to polarization of the electrodes in the solution and has been ably discussed by a number of scientists. But the polarization in the battery itself does not appear to have been investigated. After an element has been on a closed circuit for a long time, if the circuit be opened for a few minutes, on closing it, the galvanometer will at first indicate the maximum quantity due to the element, but in a few seconds the needle will gradually recede and stand as before. It appears that when the specific gravity of the s. z. approaches saturation it becomes charged with electricity like a Leyden jar or prime conductor. From numerous experiments, we find q. reaches its maximum when the specific gravity of the s. z. is between 20 and 30° B. However, for practical purposes the battery gives essentially the same force between 15 and 38° B. Below 15° B. the conducting power of the s. z. is considerably less, and consequently the resistance greater, and above 38° E

the resistance is again increased by polarization. The conducting power of 8. z. was found to be essentially the same between. 30 B. and saturation. At 1° B. it was one fourth, at 7° one half, and at 14° three fourths as great as for a saturated solution.

On the use of the negative metal in Daniell's Battery.-The negative metal in Daniell's battery is only useful as a conductor of the current.

For the purpose of testing the correctness of this conclusion, experiments were made with the following metals as the negative plate: 1, Copper; 2, sheet lead; 3, sheet iron; 4, sheet iron tinned (the ordinary sheet tin); 5, sheet zinc; 6, cast zinc. The s. c. was a saturated solution, and the s. z. had a specific gravity of 25° B. The quantity of electricity and the electromotive force was found to be the same for copper, lead, iron and tin. When zinc was used for both the positive and negative metal, the action was somewhat different. For two or three seconds after immersion in the s. c. there was a small negative current, after which the galvanometer needle was gradually deflected until it indicated a quantity of electricity nearly equal to the normal condition of the element. It then remained at rest for a few seconds after which it receded and stood at a degree indicating about one half the quantity. The whole time required to bring it to rest, was three minutes from the time of immersion. During the progress of the experiment the hydrogen was evolved so rapidly from the zinc immersed in the s. c. that the bubbles could be exploded by holding a lighted match near the surface of the liquid. As soon, however, as the galvanometer came to rest, the evolution of hydrogen had nearly ceased. On removing the zinc it was found covered with a loose copper powder, not reguline metal but such as is deposited when a large battery is employed to act on a small surface. This powder did not adhere closely to the zinc, but was separated by a thin layer of s. z. or hydrogen. On washing the zinc and repeating the experiment, precisely similar results were obtained. Although the zinc was capable of conducting the maximum quantity of electricity, yet the electro-motive force was considerably less than for the other metals. A careful examination of these experiments, leads us to the conclusion that the negative metal in Daniell's battery, only acts as a conductor of the electricity.

On the internal resistance of the battery.-In a battery with two liquids the internal resistance is made up of two elements, viz: the specific resistance of the liquid, and the resistance of the porous cell. Although recent writers have remarked the variation of resistance due to different kinds of earthen cells, yet

we have not learned that any one has determined separately the resistance due to the cell and that due to the liquids. By our method it is necessary to use at least two cells of different size. In these experiments three were employed

No. 1, White clay cell 0.31 inches in thickness, 6 inches in diame ter and 7 inches high.

No. 2, White clay cell 0-15 inches in thickness, 3 inches in diame ter and 7 inches high.

No. 3, Split-leather cell 0-06 inches in thickness, 5 inches in diame ter and 7 inches high, fitted to a bottom of inch pine.

The resistance of the element was first determined for each cell separately. Then the cells were placed one inside of the other and the total resistance determined as before. After which it was found for two at a time. These several determinations gave us a series of equations, involving the resistance of each separate cell together with the specific resistance of the liquids.

The following are the results expressed in an arbitrary unit.

Specific resistance of the liquids s. c. saturated solution, & 25 B. 13. From which it appears that the specific resistance of the liquids is about the same as for a white clay cell of the ordinary size.

As q. is increased by lessening the internal resistance, othe things being equal, it is apparent that the leather cells are s perior to those made of white clay.

On the construction of Daniell's battery.-For a local hat tery, where the external resistance is small, two-gallon st jars may be used for the vessel holding the s. c. solution. T negative plate is best made of sheet lead instead of copper heretofore; as it it je expensive and is easier bent in e to perforate the sheet with an

ART. XXI.-Contributions of the Massachusetts Institute of Technology. I-On Nitric Acid and Chlorate of Potassium as an Oxydizing Mixture applicable to Sulphur, Sulphids, Chromium, Arsenic, Organic Matters, etc.; by FRANK H STORER, Professor of General and Industrial Chemistry in the Massachusetts Institute of Technology.

SOME years since while studying the action of various oxydizing agents upon oxyd of chromium, I was struck by the superior oxydizing power of a mixture of ordinary nitric acid and chlorate of potassium over that of the mixtures of chlorate of potassium and chlorhydric or sulphuric acid, commonly used in analysis. Inasmuch as the fact of the great oxydizing power of a mixture of nitric acid and the chlorate had already been noticed and explained by several observers, I at that time contented myself with a simple statement of my own observations of the action of the mixture upon chromic oxyd† without referring in any way to the general value of the mixture as an oxydizing agent. Since that time, however, I have had frequent occasion to employ the mixture for effecting the oxydation of many substances, besides oxyd of chromium, such as present themselves in the ordinary experience of an analytical laboratory, and have satisfied myself that the merit of the process has not hitherto been duly appreciated.

Experience has convinced me, not only that a mixture of nitric acid and chlorate of potassium oxydizes more rapidly than the common mixture of chlorhydric acid and chlorate of potassium, but that it is really to be preferred in the great majority of cases to any of the agents ordinarily employed to effect oxydation in the wet way. Instead of occupying as now a secondary or alternative place in the treatises on analysis it ought to take precedence of the other processes of oxydation. It may be used with advantage in many instances where dry methods of oxydation are now recommended. With the excep tion perhaps of the sulphids, or other compounds, of antimony and tin, there are probably but few cases where its use will be found inadmissible.

The following notes include the results of several researches made by students of the Massachusetts Institute of Technology with the view of testing the capabilities of the process :

* Compare Gmelin's Handbook of Chemistry, iii, 61.

Proceedings of American Academy, 1859, iv, 342; Journal für pracktische Chemie, lxxx, 44.