of calcium. Therefore, a solution composed of 1074 of chloride of calcium, and 1000 cubic centimetres of distilled water, will be neutralised by an equal volume of a second solution made of 10 grammes of the standard soap, 100 cubic centimetres of alcohol, and sufficient distilled water to make up 1000 cubic centimetres. The addition of the smallest excess of soap solution will of course give the persistent froth as in Clark's test. M. Pons applies his process as follows:-10 cubic centimetres of the standard solution of chloride of calcium, and about 20 cubic centimetres of distilled water, are placed in a stoppered bottle, capable of holding 60 or 80 cubic centimetres. Ten grammes of the soap to be analysed are dissolved in 100 cubic centimetres of alcohol. Earthy and insoluble matters will be separated in this part of the operation, and after washing with alcohol can be weighed and analysed if required. The soap solution is now diluted with sufficient distilled water to make 1000 cubic centimetres, and the mixture is added to the lime solution from a burette graduated in cubic centimetres, and tenths of a cubic centimetre. When the persistent froth is arrived at, the amount of soap solution used is read off, and the richness of the soap experimented upon, as compared with that of the standard soap, is found by dividing 10 cubic centimetres by the number of the cubic centimetres employed. If the number used is 10 cubic centimetres, the sample is as rich as the standard; if 20 cubic centimetres are employed, the richness is only 10ths, or 50 per cent. of the standard, and so on. On the Supposed Nature of Air prior to the Discovery of Oxygen, by GEORGE F. RODWELL, F.C.S. (Continued from vol. xi., page 294.) XIII. Boyle's Second Pneumatical Treatise.-It will be remembered that Boyle's first series of "PhysicoMechanical Experiments Touching the Air" appeared in 1660; in 1661 he presented his air pump to the Royal Society, and during the five following years he undertook no lengthy pneumatical research. Occasionally, however, during this period we find mention of vacuum experiments shown by him at meetings of the Royal Society; but now that the air pump had passed out of his possession, it is obvious that he had not the same facilities as before for carrying out a research of any magnitude. Inasmuch as during these five years Boyle heard of only two air pumps having been constructed, and of only one or two new vacuum experiments, he determined to construct a new air pump, and to proceed further with his former experiments. With the assistance of Hooke he constructed an air pump in 1666, of different form from the first one, and in some respects superior to it. In order that the two may be compared, we have placed them side by side in the accompanying woodcut. Fig. 1 represents the instrument constructed in 1659, which was employed for the first series of experiments (described in the fourth and fifth of these papers); Fig. 2, the second air pump constructed in 1666, and employed for the experiments detailed below. A, Fig, represents the receiver, a globe of glass of the very large capacity of "thirty wine quarts;" it had a circular opening above, into which was cemented a brass ring, B, closed by an accurately turned disc of brass, which fitted into it, and could be readily removed for the introduction of objects to be experimented upon; the disc was perforated, and the orifice closed by a ground brass stopper, C, by turning which, bodies within the receiver connected with it by a string could be moved when the receiver was exhausted. The lower part of the receiver communicated directly with the cylinder, D, and was furnished with a stopcock, E; a solid piston, moved by a rack and pinion, worked within the cylinder. In the upper part of the cylinder there was an orifice, into which the brass stopper, F, fitted air-tight-this served as a valve. Suppose the piston at the top of the cylinder, the stopper, F, in its place, and the stopcock, E, closed, the piston is drawn to the bottom of the cylinder (that is to say, to the position shown in the figure), and E is opened, immediately part of the air in the receiver rushes into the vacuous space in the cylinder, E is then closed so as to shut off communication between the cylinder and receiver, F is removed, and the piston forced to the top of the cylinder, the air within the latter escaping through the valve orifice; F is now replaced, and the previous operation repeated until the receiver is exhausted. A (Fig. 2) represents a cylinder of metal, furnished with a piston moved by rack and pinion. The valve (F, Fig. 1) of the 1659 air pump was in this transferred to the piston, which was perforated, and the orifice was closed by a brass stopper with a long handle, B, for the purpose of placing it in the orifice when the piston was at the bottom of the cylinder. A pipe provided with a stop cock, C, issued from the side of the cylinder, and passing along the air pump plate, D, terminated beneath the receiver, E. The piston being at the bottom of the cylinder, the stopper in its place, and the stop cock C closed, the piston is raised to the position shown in the figure, and C is opened, immediately air from the re NEWS ceiver flows into the vacuous space in the cylinder; C is now closed, the valve opened by raising B, and the piston forced to the bottom of the cylinder; the stopper is then replaced, and the previous operation repeated until the desired effect is produced. The advantages of Boyle's second air pump over the first were (a) the diminished size of the receiver as compared with the pump barrel, whereby the exhaustion was rendered more complete, and was more quickly obtained; and (b) the introduction of an air pump plate, whereby the use of a globular receiver was avoided, and bodies to be experimented upon, instead of being suspended, could be placed upon a level surface, and thus during the working of the instrument did not multiply its smallest motion by swinging, as was the case when suspension was resorted to. The air pump plate was of iron, and the receiver was cemented to it, by which means Boyle managed to retain a receiver well exhausted for a length of time. The vacuum produced by the second pump appears to have been very good, of which we shall have several opportunities of judging as we proceed; the chance of leakage, moreover, was less than in the first pump. Nevertheless, the 1666 instrument had its disadvantages; like its predecessor, it fell short of Otto Guericke's pump in one respect-the valves were worked by the hand, which rendered the operation of pumping comparatively slow; it was also inferior to the 1659 air pump in one respect-the pump barrel was placed in a vessel of water, and the piston always worked under water, which not only rendered the instrument cumbersome, but not unfrequently led to water finding its way into the receiver. In describing his first air pump, Boyle mentions as a special reason why he endeavoured to construct an instrument different from Otto Guericke's that he desired to avoid the necessity of having it work under water; it is curious, therefore, that in this second pump, after further experience, he adopts that which he had previously considered so great a disadvantage. In 1669 Boyle published a volumet containing an account of his new air pump, and of a number of experiments made therewith; it is written in the form of a letter, and is dated March 24, 1667. This second pneumatic treatise cannot be read with the same amount of interest as the first, for there is not only less original matter, but many of the experiments are mere repetitions of those described in the former treatise, and for the most part tend to strengthen results previously obtained, and to prove or disprove conjectures; but be it remembered we depreciate this work only as compared with the first treatise, for no research on pneumatics comparable to it had appeared since the first research of the same author, which excelled it. We will briefly consider the more important experiments described in the second treatise : Experiment 1-A phial of about five ounces capacity was partially filled with mercury; a tube four feet long open at both ends was then cemented air tight into its neck in such a manner that it reached nearly to the bottom of the phial, and consequently passed beneath the surface of the mercury; it is obvious that when the air within the phial expands, it must cause the mercury to rise in the tube. The arrangement was placed under "A continuation of new experiments, physico-mechanical, touching the spring and weight of the air, and their effects. Part I. By the Honble. Robert Boyle, F.R.S. Oxford, 1669."-Although dated 1669, this work was published in the latter part of 1668, as appears from the copy in possession of the Royal Society, on the title-page of which is written-"Presented from ye author to ye R. Society, Novemb. 30, 1668." a tall receiver, which was exhausted; when the most complete exhaustion had been attained, the mercury in the tube had risen to a height of twenty-nine inches above that in the phial. When the air vessel was very large the mercury rose no higher than twenty-nine inches, (Experiment 2); neither did variations in the diameter of the tube alter the case, (Experiment 3). Experiment 4. Water was substituted for mercury in the above arrangement, on exhausting, it was ejected forcibly from the top of the tube by the expansion of the air in the phial-the "fountain in vacuo" of our present works on pneumatics. Experiment 8. A bladder one fourth filled with air was securely closed, and introduced into a receiver; it was loaded with a weight of 28 lbs.; on exhausting, the expansion of the air within the bladder raised the weight. Experiment 11. A tube 50 inches long was bent at a right angle, its upper portion was placed in air tight connection with the receiver, while its lower end dipped into a vessel of mercury; on exhausting, mercury rose to a height of 29 inches in the tube. This arrangement was afterwards applied by Hauksbee to measure the degree of rarefaction obtaining in a receiver, and is now known as the "barometer guage." Experiment 12. In order to prove that the height to which a liquid is raised in a vacuous tube by the pressure of the external air, depends upon the specific gravity of the liquid, Boyle procured a glass U tube, the length of each limb of which was 42 inches; it was inverted, one limb was caused to dip into mercury, the other into water, and the upper part of the tube was placed in connection with the receiver; on exhausting until the water had risen to a height of 42 inches, the mercury in the other limb was found to have risen 3 inches; when strong brine was substituted for mercury, the brine column stood at 40 inches, a solution of potash stood at 30 inches, the water column being in each case at 42 inches. Experiment 13. Into a pint bottle Boyle poured mercury and water, so that they together partially filled it; two upright tubes, open at each end, were then cemented side by side into the neck of the bottle, one reached beneath the mercury surface, and the other beneath the water surface; the arrangement was placed under a receiver; on exhausting, it was found that when the elasticity of the air in the phial had raised the mercury to a height of 1 inch in the one tube, the water had risen to a height of nearly 14 inches in the other; when the mercury was at 2 inches, the water was at nearly 28 inches." Experiment 14. A short tube closed at one end was filled with mercury, and inverted into a vessel of mercury; a longer tube was filled with water and inverted into a vessel of water; both vessels with their tubes were placed under a tall receiver; on exhausting, it was found that when the mercury in the tube had fallen to within 3 inches of the stagnant mercury, the water column stood at 42 inches, with the mercury at 2 inches, and 1 inch respectively, the water fell to 28 and 14 inches. Experiment 15. In order to determine the exact height to which water can be raised by a suction pump, the air pump was conveyed to the roof of a house, and a tube bent twice at a right angle was placed in airtight connexion with the receiver. The longer limb of the tube was 35 feet long, and its lower end was caused to dip into a vessel of water standing on the ground. On exhausting, the water rose to a height of 33 feet, the mercury column in a barometer standing at 29 inches. This experiment, together with several of the above, prove the great efficiency of the 1666 air pump. Experiment 16. In order to ascertain whether air contributes to the elasticity of solid bodies, a piece of whalebone having a weight attached to one end of it was placed in the receiver in such a manner that it supported the weight just above the air pump plate. On exhausting no alteration in the position of the weight was observable. (To be continued.) PHOTOGRAPHY. NEWS parallel lines and consequently converged to one focal point, and what parts do not conform to this condition, and also the amount of divergence. On applying this test I found that an objective of flint and crown in which the visual was united with the photographic focus, (in other words, where the instrument could be focalised on a plate of ground glass by the eye, as in ordinary cameras, and in the heliographs constructed by Dalmayer for the Kew Observatory and for the Russian Government), is a mere compromise to convenience, in which both the visual and actinic qualities are sacrificed. In order to bring the actinic portion of the spectrum Astronomical Photography, by LEWIS M. RUTHERFURD. between parallel borders, i.e., to one focus, it is necessary (Continued from page 51.) that a given crown lens should be combined with a flint which will produce a combined focal length about oneIn the autumn of 1861 I began to experiment with a tenth shorter than would be required to satisfy the conreflecting telescope with silvered mirror, which recomditions of achromatism for the eye, and in this condition mended itself both by the simplicity and ease of its conthe objective is entirely worthless for vision. struction and the entire freedom from dispersion. One Having obtained the achromatic correction, I had a was mounted of thirteen inches aperture and eight feet most delicate task to produce the correction for figure, focus, of the Cassegranean form. It was ground and since the judgment of the eye was useless unless entirely approximately figured by Mr. Fitz, and in its frame, as protected from the influence of all but the actinic rays. strapped to my large tube and carried by the equatorial A cell of glass enclosing a sufficient thickness of the clock, weighed less than fifteen pounds. Many modes cupro-sulphate of ammonia, held between the eye and were tried of silvering, but the best results were the eye-piece, enabled me to work for coarse corrections obtained by Liebig's process, wherein the silver is upon a Lyra and Sirius, but so darkened the expanded deposited from an ammonia nitrate solution by sugar of disk of a star in and out of focus that all the final cormilk. After three months' trial I abandoned this instru-rections were made upon tests by photography, which ment as unfit for use in my observatory. First the tremors of the city, quite imperceptible in the achro-face to be combated. Still, however, the process was gave permanent record of all the irregularities of surmatic, were, by the double reflection, increased about long and tedious, dependent upon but three stars as thirty-six times, an insurmountable obstacle to good tests, and they too often obscured by bad weather. My work. Secondly, the silver deposit is so easily attacked, mode of correction was almost entirely of a local nature, both by moisture and the gases which abound in the such as practised by the late Mr. Fitz and Mr. Clark for city, as to make it necessary to re-silver the speculum at least every ten days, a labour not to be contemplated with equanimity. Dr. Draper has found the silver surface very much more durable in the dry, pure air of the country. I regard the Cassegranean form as the best adapted to lunar photography, since the dimensions of the image can be varied at will, as circumstances dictate, by simply changing the small mirror, a number of which might be kept at hand. Having thus failed in astronomical photography with an ordinary achromatic, with a correcting lens and with a reflector, I began, in the autumn of 1863, the construction of an objective, to be corrected solely with reference to the photographic rays. In a former communication to this journal, January, 1863, I drew attention to the peculiar adaptation of the spectroscope as a means of examining the achromatic condition of an objective, and since it was principally by the aid of this instrument that I have been enabled to procure a fine photographic correction, I may be pardoned for touching again upon this application. The image of a star at the focus of a perfectly corrected objective would be a point, the apex of all conceivable cones having the object glass, or parts of it, as the bases. This point falling upon a prism would be converted in a line red at one end and violet at the other, with the intermediate colours in their proper places. If, however, the different coloured rays are not all brought to the same focus, the spectrum will no longer be a line, but in the uncorrected colours will be expanded to a brush the width of which will be the diameter of the cone where intercepted by the prism. It will thus be seen that a simple glance at a star spectrum will indicate at once what parts of the spectrum are bounded by many years. I This objective was completed about December 1 last; with a few inches shorter focal length, and can be subit has the same aperture, 111 inches, as the achromatic, stituted for it in the tube with great ease. The corrections of this objective are such that I think it capable of picturing any object as seen, provided there be suffcient light and no atmospheric obstacles. As respects the light, I have obtained images of stars designated by Smyth as of the 8 magnitude, and other stars on the same plate of full a magnitude lower. In the cluster Prosepe, within the space of one degree square twenty-three stars are taken, many of which are of the ninth magnitude, with an exposure of three minutes. An exposure of one second gives a strong impression of Castor, and the smaller star is quite visible with half a second. With the achromatic objective it was necessary to expose Castor ten seconds to obtain a satisfactory result. The great obstacle which prevents the results of photography from realising the achievements of vision is atmospheric disturbance. In looking at an object the impression is formed from the revelations of the best moments, and it is often the case that the eye can clearly detect the duplicity of a star, although the whole object is dancing and occillating over a space greater than its distance. The photograph possesses no such power of accommodation, and the image is a mean of all the conditions during exposure. It is, therefore, only on rare nights in our climate that the picture will approach the revelations of the eye. Since the completion of the photographic objective, but one night has occurred (March 6), with a fine atmosphere, and on that occasion the instrument was occu pied with the moon; so that as yet I have not tested its powers upon the close double stars, 2" being the nearest pair it has been tried upon. This distance is quite manageable, provided the stars are of nearly equal magnitude. The power to obtain images of the ninth magnitude stars with so moderate an aperture promises to develope and increase the application of photography to the mapping of the sidereal heavens, and in some measure to realise the hopes which have so long been deferred and disappointed. It would not be difficult to arrange a camera box capable of exposing a surface sufficient to obtain a map of two degrees square, and with instruments of large aperture we may hope to reach much smaller stars than I have yet taken. There is also every probability that the chemistry of photography will be very much improved, and more sensitive methods devised. On March 6 the negatives of the moon were remarkably fine, being superior in sharpness to any I have yet seen. The exposure for that phase, three days after the first quarter, is from two to three seconds, and for the full moon about one-quarter of a second. The success of this telescopic objective has encouraged me to hope that an almost equal improvement may be made for photography in the microscope, which instrument is more favourably situated for definition than the telescope, since it is independent, of atmospheric condi. tions. Its achromatic status is easily examined by the spectroscope, using as a star the solar image reflected from a minute globule of mercury. Mr. Wales is now constructing for me a one-tenth objective, which, upon his new plan, is to be provided with a tube so arranged as to admit of the removal of the rear combination, and, in place of the one ordinarily used, one is to be substantiated at will which shall bring to one focus the actinic rays.-American Journal of Science, xxxix., 304. PROCEEDINGS OF SOCIETIES. COLLEGE OF PHYSICIANS. Friday, April 28, 1865. the palmitic, margaric, and stearic acids are mild inactive solids. In comparing formic acid with palmitic acid, which is only two-thirds of the way down the list, we scarcely perceive a single point of resemblance; but in comparing formic acid with the acetic, or still more and stearic acids, the difficulty is rather to see the differdecidedly in comparing palmitic acid with the margaric ence than the resemblance between them. Nevertheless, between the upper and lower members of the series there is a latent similarity, and indeed certain well marked properties are common to all the acids under consideration. They are all volatile, inflammable, saponifiable, monobasic, and decomposible in a similar manner under the influence of the same reagents. We are not in in the habit of regarding vinegar in any form as an inflammable material, but in reality strong acetic acid is almost as inflammable as alcohol. It only requires to be heated externally for a few minutes, when it burns as you perceive with a large, lambent, feebly luminous flame. Neither are we in the habit of regarding the acetates as soaps, yet solutions of acetates possess the property of forming a persistent froth or lather to such an extent as to be highly characteristic; so that by searching out for latent resemblances we perceive that the different members of the series from the top to the bottom are associated with one another in a very intimate manner. The primary aromatic acids at present known are far less numerous, and the series consequently far more limited, as shown in the table: The first on the list is collic acid, a product of the artiNext we have ficial oxidation of albuminous matter. benzoic acid, which is usually regarded as the representative in this series of acetic acid in the fatty series. This is followed by two acids of which at present comparatively little is known, namely, the toluic and picic; while the series is terminated by cuminic acid, a product formed by the spontaneous oxidation of the chief constituent of oil of cumin. Now, just as the acetic and propionic acids are "On Animal Chemistry." A course of Six Lectures by associated each with their respective hydrocarbons, WILLIAM ODLING, M.B., F.R.S., F.R.C.P. LECTURE 2. (Concluded from page 55.) The primary monobasic acids are nearly all of them capable of being distributed into two principal series, known as the fatty and aromatic series respectively. To the series of fatty acids, beginning with the formic, acetic, and propionic acids, I have already directed your attention. You observe that each successive member of the series differs in composition from its predecessor by an increment of atom of carbon and 2 atoms of hydrogen. Bodies in which this difference of CH2 prevails are said to be homologous, and the series of fatty acids is accordingly spoken of as a homologous series. You observe (vide table of monatomic fatty acid series) that from the first to the twenty-first term, the series is complete, while between the twenty-first and the thirtieth terms only one intermediate acid is known, namely, the cerotic acid, an important constituent of ordinary beeswax, and especially of the Chinese wax, secreted by an insect of the coccus tribe. Now, while the difference in composition and properties, between the acids at either extremity of this series is extremely marked, that between any two or three consecutive acids, more especially of those low down in the list, is so slight as to be scarcely appreciable. Thus the formic and acetic acids when in a state of purity are perfectly mobile, strongly corrosive liquids; the butyric, valeric, and caproic acids are thin oils, while alcohols, aldehydes, and more highly oxidised acids, as shown in the tables to which I have already adverted, so is every other primary monobasic acid, both of the fatty and aromatic series, associated with a more or less complete set of congeners, having to it the same relations of composition, properties, and mutual metamorphosis, that the various members of the acetic and propionic families have to the acetic and propionic acids respectively. Here, for example, are tabulated the principal compounds which are associated in this manner with benzoic acid :Benzoic Group. Accordingly, when we break up any complex animal product into its simpler constituent molecules, by an absorption of water, we are always, or nearly always, able to refer each of the completed molecules to its appropriate position in some homologous series and in some heterologous grouping; just as we accord to common alcohol its proper place both in the series of alcohols and in the group of acetic compounds. Now, let us apply these several considerations to unravel the composition and relationship of some particular animal product, say hippuric acid, of which a very beautiful specimen, kindly lent me for the occasion by Messrs. Hopkins and Williams, is now on the table before you. Hippuric acid, the molecule of which is represented by the very complex formula C,H,NO, and is composed, therefore, of 22 constituent atoms, is now known to consist of a residue of benzoic acid, a residue of oxiacetic or glycolic acid, and a residue of ammonia united with one another in a particular manner. Ammonia undergoes a very remarkable decomposition when acted upon by nitrous acid, its hydrogen being transformed into water and its nitrogen liberated in the gaseous state, thus: H2N+HNO2=2H2O+N2. Accordingly, when hippuric acid is treated with nitrous acid, the ammoniacal residue is similarly destroyed by the nitrous acid, while the two other residues are left combined with one another in the form of benzoglycolic acid. Hence, hippuric acid has been represented as a combination of ammonia with benzoglycolic acid, which is itself susceptible of decomposition into its constituent benzoic and glycolic acids Hippuric acid. The positions of the benzoic and glycolic acid in the groups and series to which they belong have been already referred to the benzoic being the second on the list of the primary | aromatic acid series, the glycolic being second on the list of the carbonic acid series-the former being the pivot of the benzoic, the latter a member of the acetic group. Our actual knowledge, then, of the constitution of hippuric acid amounts to this, that it contains the residues of three distinct molecules, which by an absorption of water are capable of being obtained separate from one another. When any one of these residues is destroyed or You observe that by subtracting two atoms of water removed the other two residues are left in combination, from the sum of the atoms of carbon, hydrogen, nitrogen, and accordingly by treating hippuric acid with different and oxygen contained in the three molecules of benzoic reagents we may obtain the benzoic and ammoniacal acid, oxiacetic acid, and ammonia, there is left a compound residues in the form of benzamide, or the benzoic and having the formula of hippuric acid. Now there are few glycolic residues in the form of benzoglycolic acid, or the bodies about whose intimate constitution greater varieties glycolic and ammoniacal residues in the form of sugar of of opinion have been maintained than with regard to gelatine. To this much, which is certain, a something hippuric acid. Each successive chemist who examined may be added which is probable. From many considerations the body acted upon it with a different reagent, and into which I cannot at present enter, it seems, at any rate, accordingly as the special reagent employed attacked one that the ammoniacal constituent of hippuric acid is actually or other of the different residues entering into the consti- in more intimate association with the glycolic than with tution of the acid, so was a different hypothetical formula | the benzoic residue, so that the composition of hippuric |