employed in compressing the air. Let us now apply these principles. to computing the head in experiment 1. Head lost at entrance, 1.000 feet. Table II contains the results of this calculation applied to all the experiments. The computed head falls short of the observed head in the experiments with velocities exceeding 3 feet per second, as was to be expected, since in these cases large quantities of air were carried past the chamber, involving resistances not taken account of in the computation. Moreover, in these cases, air counting as water, the tendency is to over-estimate the quantity passing the weir. One thing is especially to be noted. In the experiments giving the best results the agreement is quite satisfactory. We may, therefore, I apprehend, apply this method, with a good degree of confidence, to a system of practical size, understanding always that it is working to its best advantage. For a system of practical size, we may fix the following dimensions: Descending shaft, 10 feet diameter, making the mean radius six times that of the model. Ascending shaft in same proportion. Depth,. 120 feet, corresponding to a pressure of about 50 pounds per square inch, making the journey of the water about four times that in experiment 5. Fall, 15 feet. Velocity in descending shaft, 6 feet per second. It would not be advisable to make such a system an exact copy of the model which, owing to the limited space, could not have the form best calculated to avoid loss of head. The loss of head in experiment 5 was 0.98 foot, with a velocity of 4.49 feet per second. The loss in the straight passages, by the best formulas, could not have exceeded The loss due to bends, chiefly the bend at the bottom of the descending shaft, which the results show to be more abrupt than necessary, was A loss also occurs at the entrance, 0.200 foot.. 0.250 66 0.68 being the coefficient of contraction of the water at 0.980 is a part of the head due to the initial velocity which, it is evident, was not wholly suppressed, the enlargement of the channel under the air chamber being a little too abrupt. This is evident, also, from the readiness with which air was carried past the chamber, implying commotion in the water, which retarded the elimination of the air. The item 0.365 might have been wholly suppressed by suitably rounding the entrance to the descending shaft. We will therefore reject it in applying the results to the proposed system. The frictional head proper (0-200) is directly proportional to the square of the velocity, directly as the distance traversed by the water, and inversely as the mean radius of the channel. The other items of head (0.250+0·165=0·415) are directly as the square of the velocity.. The losses in the proposed system of channels will therefore be as follows: Head expended in reducing the water to foam, 1.000 4.49 66 Similarly, with a head of 30 feet, reducing the air to a pressure of 100 pounds per square inch, the efficiency would be 81 per cent. St. Paul, July, 1880. Stability of Oxygenated Water. - Berthelot experimented upon a liquid containing 3.85 grammes of oxygen per litre (225 grains per gallon), to which 15 gramme (48 oz.) of sulphuric acid had been added. When exposed to a temperature ranging between 10° and 15°C. (50° and 59°F.), the decomposition continued, during the first month, in a ratio nearly proportional to the time. Afterwards the reaction gradually diminished, and some samples which were prepared in December, 1877, still include measurable quantities of oxygenated water. When the oxygenated water is pure, or very concentrated, the decomposition at first is much more rapid than would be indicated by a simple proportionality to the time. Then comes a certain consecutive period when such proportionality exists; finally, the reaction diminishes nearly as if following a curve with an asymptote. Similar relations are found in the study of ozone, and probably in every exothermic decomposition which is slowly effected in a homogeneous medium. The velocity of the transformation varies in an extraordinary manner with the presence of foreign substances in the liquid. For example, a liquid enclosing 1.66 grammes of active oxygen per per litre, acidified by 009 gramme of chlorhydric acid, was decomposed with only one-fifth of the rapidity of that which contained the sulphuric acid.-Comptes Rendus. C. EXPERIMENTS ON THE STRENGTH OF YELLOW PINE. By Prof. R. H. THURSTON. [Presented to the American Association for Advancement of Science, Aug., 1880.] In a paper read at the Saratoga meeting of the American Association for the Advancement of Science the writer presented the result of a series of experiments on the strength of timber, in which were given several unusual figures.* To determine how far these results were due to peculiarities of the selected samples supplied from the Navy Yard, and to determine to what extent size affects the resistance, a more extended series of transverse tests were made, and the results of experiments upon yellow pine, of the ordinary market qualities and of various dimensions, are now presented below, as determined in the Mechanical Laboratory of the Stevens Institute of Technology. In the paper referred to, the modulus of elasticity was given for yellow pine as an extraordinarily high figure. It will be observed that the best wood here described gives also very high values of E, and a comparison of the pieces of the first with these test specimens shows the selected Navy Yard specimen to have been of better material than either of the latter. Samples marked F1, F2, F3, were from the same plank—a piece of yellow pine cut in Georgia, April, 1879, and tested after several months of seasoning, when it had become thoroughly dry. The three specimens were considered good material. F, was not straight-grained and broke obliquely, giving a much lower modulus of elasticity, as well as of mixture, than its companion specimens. 3 Samples B1, B2, B3, were cut from a stick ten inches square in section, which had been lying under cover, seasoning, nine or ten years. Numbers 1 to 12, inclusive, were small sticks sawn out of the middle of a plank, originally four inches thick, one foot wide, and twentyfour feet long. A stick was first cut three inches square and twentyfour feet long, which was then cut into strips of varying smaller dimen * Among these were several due to printers' errors, which, owing to the illness of the writer, were not corrected in proof. The tenacity of yellow pine, for example, was made 2070-2 when it should have been given at 20-702. sions. The wood was selected from lumber yard stock, and was considered to be fairly representative of average timber. It was cut in Florida, in October, 1879, and reached Hoboken in January, 1880. Specimens 1 to 8, inclusive, were too green for use in construction; Nos. 9, 10 and 11 were kiln-dried 56 hours, at a temperature of 130° Fahr., No. 12 was dried 12 hours, at 210° Fahr., at which temperature the pitch exuded from the wood quite freely. Still another specimen, not here recorded, was heated 1 hours at 420°F., and was somewhat charred. Under test it gave a modulus of rupture, R = 9000. In the table containing a resumé of results is also given the figures obtained in the earlier experiments on selected Navy Yard material, marked J and those of a sample, K, tested by another observer.* Specimens A, A,, were picked up in a workshop, and used simply to determine specific gravity; they were probably not the best Southern long-leaved pine, such as it was intended that the samples tested should be. Calculating E = W B 4 Abd3 for heavy loads and considerable deflec tions, the following figures were obtained for this pseudo-modulus : TABLE II.-Values of E at one-third to one-half Total Load. These figures differ little from those obtained by calculation from the smaller deflections and loads. It was observed that this modulus sometimes decreases with increase of spring, and sometimes increases. As a general rule, the maximum figure was given at one-third, rarely at one-half, and about as often at the beginning of the test. The latter case occurred most frequently with the unseasoned timber. * Van Nostrand's Magazine, Feb., 1880, p. 166. |