of the graduation, and by Grunow's cathetometer fine adjustment, the terminal lines of the eye-piece micrometer are made to coin. cide with two millimetres of the graduation. The focussing movement now moves the microscope so that distinct vision is had of the meniscus, and the level of the mercury is read to the hundredth of a millimetre on the eye-piece micrometer, whose divisions now represent the divisions of the tube carried forward into its interior. A four inch objective, with an amplification of about sixty diameters, is thus utilized. F. The probable error of this reading of the level of the meniscus cannot be separated from other probable errors incident to the observation, but the sum total of all the errors whatever is equivalent to no more than a probable error of one-hundredth of a millimetre in this determination: and in the calibration of the apparatus, made before much practice in the use of this reading arrangement, the probable error of a reading was the hundredth of a millimetre. G. The probable error of a single determination of oxygen in air is less than the four hundredth of one per centum. H. The method of measurement is adapted to rapid computation. The whole reduction of three measurements in an analysis, so as to get the per centum of oxygen, takes less than two and a half minutes. NUMERICAL RESULTS FOR THE MEAN RATIO OF OXYGEN TO THE SUM OF OXYGEN AND NITROGEN IN ATMOSPHERIC AIR. By EDWARD W. MORLEY, of Hudson, Ohio. [ABSTRACT.] SINCE the proportion of oxygen to nitrogen in the air varies almost as incessantly as its temperature or pressure, the mean value can be accurately ascertained only by regular and continuous observation. The true value cannot be safely inferred from observations at irregular intervals. A series of daily analyses in duplicate, continued for six months, undertaken for a very different purpose, may therefore be of some interest as contributing to the knowledge of this constant. The result is affected with errors depending on the following causes, the probable magnitude of which is well known. 1. The most serious uncertainty depends on the uncertainty in the calibration of the eudiometer. The probable error of a single determination at any given point on the scale is three milligrammes of water. At each point four determinations were made, so that it is as likely as not that the volume at any given point is known within a milligramme and a half of water. The probable error of the mean result, as far as this error depends on errors of calibration, is 0.0014 per centum. 2. The second source of uncertainty depends on the fact that the composition of the air is variable. Owing to this variation, the result of the number of samples analyzed is as likely as not to differ from the result from an unlimited number of samples by 0.0009 per centum. 3. The third source of uncertainty depends on the accidental errors of analysis. Owing to these errors, the mean result obtained from two analyses of each sample is as likely as not to differ from what would have been obtained by an unlimited number of duplicate analyses of each sample by 0.0002 per centum. This result is also affected with one source of constant error which has not yet been taken into account. This error is due to the fact that the eudiometer tube, after the explosion, contains a larger volume of water than at the previous measurement. I do not see clearly how to determine the magnitude of this error. It is at present hoped that other sources of error produce only results which may safely be neglected in comparison with these. The mean composition of the air, and the magnitude of the errors attending the determination, may then be stated as follows: Ratio of oxygen to sum of oxygen and nitrogen, 20.949 per ct. Probable error from imperfect calibration, Probable error from variation in ratio, Total probable error, 0.0014" 0.0009 66 66 66 SOME CONCLUSIONS AS TO THE CAUSE OF THE FREQUENT FLUCTUATIONS IN THE RATIO OF OXYGEN TO NITROGEN IN THE AIR AT DIFFERENT TIMES. By E. W. MORLEY, of Hudson, Ohio. [ABSTRACT.] To study the subject above indicated, I have made duplicate analyses of air collected at Hudson, Ohio, on every day from January 1st to June 30th. The results have been graphically compared with the daily observations on temperature and pressure of the atmosphere made by the Signal Service at Cleveland, Ohio, from which Hudson is not far distant. Many of the variations in the amount of oxygen observed are closely connected with variations in the temperature and pressure. For the prediction or explanation of these, local observations of temperature and pressure might be sufficient. I have also been favored, through the courtesy of General Myer, with the thrice-daily maps of the state of the weather for the period mentioned. From a comparison between these maps and the results of my analyses, which I have only this week begun, I derive some interesting conclusions, serving to confirm the notion that most of the variations in the amount of oxygen are caused by the vertical descent of air from above. I find this notion strikingly confirmed in some cases where it was some time since evident to me that Loomis' suggestion that the cold was caused by the descent could not be accepted as holding good. I find evidence that some depressions of temperature are caused by such descent, and at such times the amount of oxygen falls promptly at the beginning of the cold. But with the times of depression of temperature remarkable for their suddenness and severity, a vertical descent of cold air seems to be the effect and not the cause. The descent follows the cold by a day or two or more, and at the time when the Signal Service maps lead me to suppose the descent has begun, and not till then, the fall in oxygen occurs. The variations found this year have not been as great as those published by me last year, nor as great as those found by Jolly. I have therefore carefully re-examined those made before this year, and am confirmed in my confidence that they are affected with no unsuspected error. THE SOIL SUPPLY OF NITROGEN FOR PLANTS. By W. O. ATWATER, of Middletown, Conn. [ABSTRACT.] THE nitrogen of the soil, which is the chief source of supply of that material to plants, is subject to more or less loss by the leaching away of nitrates to the lower strata of the soil and thence to rivers and the sea. The best data at present at hand indicate that, in certain portions of the United States, e. g., in New England, a much smaller portion of the total water which comes to the soil thus escapes by percolation than is the case in England and northern Europe. A larger proportion of the summer rainfall is evaporated from the New England soil, and probably, in our longer and colder winter, the freezing of the ground would do more to prevent downward escape of water here than there. Accordingly, other things being equal, we might assume a probability of less loss of nitrogen by the leaching away of nitrates from our soils than from those of northern Europe. If such be the case, our soils, in the regions that have been exhausted by cultivation, might be expected, ceteris paribus, to be the richer in nitrogen. In northern Europe, according to general experience, nitrogenous fertilizers are held to be equally or more important for the increase of crops in ordinary husbandry than phosphatic, potassic, or other mineral manures. So far as the less definitely measured experience of our agriculture indicates, nitrogen hardly appears to assume a position so important relatively to other ingredients of plant-food as is the case in Europe. A series of field experiments with chemical fertilizers, executed by several agricultural colleges and private individuals, upon a plan suggested by the writer, have had for their chief end the study of the effects of nitrogenous materials upon the growth of plants in various soils in New England and other states. The general outcome of these shows a decidedly less relative benefit from nitrogen and more from phosphoric acid, potash, etc., than the teachings of European experience and experiments would lead us to expect. This fact, though in the nature of the cause less definitely attested than strict scientific reliability would require, does nevertheless, so far as it goes, corroborate the assumption that our soils are better able to supply our crops with nitrogen than is the case under corresponding circumstances in Europe, and in lack of better explanation we may not be entirely wrong in attributing the difference, in part at least, to the climatic conditions which produce a smaller percentage of percolation of water of atmospheric precipitation here than in Europe. Our agriculture suffers, in comparison with that of some other regions, through dry weather and more frequent drought. Nitrogen is of immense importance in agriculture and its lack can be supplied only at immense cost. If the hypothesis above suggested be correct, we have in the fact which it explains a partial compensation for the loss which our lack of atmospheric water-supply entails upon us. THE DETERMINATION OF PHOSPHORIC ACID BY THE MOLYBDIC METHOD. By W. O. ATWATER, of Middletown, Conn. [ABSTRACT.] I. EFFECT of presence of organic matter upon the precipitation of ammonium phospho-molybdate. It has been stated (e. g., by Schumann, Fres. Zeit., 14, 301) that phosphoric acid may be accurately determined by precipitation with ammonium molybdate, in presence of organic matter. But analyses are adduced showing that the determination may be materially affected by organic matter, even after treatment with strong nitric acid. The organic matters were found, in a number of cases, to partially prevent the precipitation of the phosphoric acid. II. Precipitation of small quantities of phosphoric acid in the presence of alkaline salts. It has been shown that the precipitation of phosphoric acid as phospho-molybdate is hindered by certain compounds, as hydrochloric acid, sundry sulphates, etc., and aided by nitric acid, ammonium nitrate, and the ordinary solution of ammonium mo |