by gradual oxidation, is capable of affording us with regard to the molecular constitution of bodies. This question is best answered by considering how many isomers it is capable of revealing to us in any one case. Take for instance amyl-alcohol. We know that there are many possible isomers of this body, but gradual oxidation, or at least oxidation carried far enough to produce those substances which we have agreed to term proximate products of oxidation, could only reveal to us the existence of a portion of them; for it is obvious that we may have a pseudo-primary amylalcohol, i.e., an alcohol containing a pseudo-amyl, say for instance propyl-ethyl; and we may have a secondary amyl-alcohol containing propyl and ethyl. Both these compounds would, we believe, yield the same proximate oxidation products, though doubtless the former would, in the first instance, yield pseudo-valerianic acid. This would at once distinguish it from the real primary alcohol, but would not distinguish it from the secondary alcohol, which would yield the same oxidation-products. Still, though the socalled proximate products of oxidation would not furnish us with information on this point, the mediate products taken in conjunction with the proximate products would. We have not in the foregoing paper considered the case of bodies in which the ratio of carbon to hydrogen is such as to render it impossible to account for the whole of the carbon in the form of acids of the acetic series. It is obvicus that such bodies must either yield substances of an altogether different class, or the carbon must be converted into carbonic acid. XLV. On the Strength of Solutions of Phosphoric Acid of Various Densities. By Mr. JOHN WATTS, Senior Bell Scholar in the Laboratories of the Pharmaceutical Society. [From the Proceedings of the British Pharmaceutical Conference, 1865, p. 39.] In the compilation of a table of this kind, the first thing is to know at what specific gravity to start; accordingly, finding that a thick syrupy acid of 1.5 p. c. sp. gr. contained nearly 50 per cent. PO, I made that the starting-point, and proceeded regularly downwards as far as sp. gr. 1.006. The interval between these two numbers contains 47 specific gravities, therefore 49 in all, and as the acid of each specific gravity was analysed at least three times, in order to obtain a correct mean, it entailed the work of about 150 analyses. The table, when completed, stands as follows: 1.508 49.60 1.392 40.86 1.293 32-71 1.185 22:07 1.081 | 10:44* 1.492 48.41 1.476 1.464 1.384 40.12 1.285 31.94 1.173 20.91 47 10 1.376 39.66 1.276 31.03 1.162 19.73 45.63 1.369 39.21 1.268 30.13 1.153 18.81 1.453 45.38 1.256 38.00 29.16 1.144 17.89 1.047 1.073 9.53 1.066 8.62 1-056 7.89 1.257 6.17 I would next notice the method employed for its analysis. After essaying and testing the various advantages of a great many different processes, of which I will speak hereafter, I came to the conclusion that with a pure solution of phosphoric acid, no method is more simple, more accurate, or less liable to error, than the method employed in the British Pharmacopoeia, viz., “the evaporation down of a weighed quantity of the solution, with a known excess of pure protoxide of lead." I confess I was somewhat disappointed when first employing this method, owing to the discordant results obtained, notwithstanding that at first sight it seemed exceedingly straightforward and plain; but I afterwards found it entirely arose from not operating with pure oxide. I had used the commercial article, and though previously to each analysis it had been carefully ignited, there nevertheless remained so much carbonate and other impurities, as to render it practically worthless, no two results agreeing nearer than 2 or 3 per cent. Finding this to be the case, I looked about for some other substance to use instead, and for this purpose tried the oxide of zinc. * British Pharmacopoeia. Analysis with this latter oxide gave perfectly accurate results as regards numbers, but was open to a great objection, inasmuch as the phosphate of zinc readily fuses; and upon ignition towards the end of the analysis to get rid of the last traces of water, the fusing of the phosphate, and its adhering tenaciously to the bottom of the crucible, from which it cannot be subsequently removed, entirely spoils the vessel for a second operation. Oxide of magnesia answered no better, for this, unlike the oxides of lead and zinc, forms a hydrate when put into water; and, as is the case with many magnesia salts, either the last traces of this water of hydration, or the atom of basic water assimilated when neutralizing the phosphoric acid, is so difficult to expel totally, even after powerful ignition, that one can never be certain that the whole of the water is driven off, unless the capsule has been allowed to cool and re-ignited several times; which, with such a number of similar analyses, causes much unnecessary trouble. The volumetric nitrate of uranium process was also tried, but as the results never approached nearer than 5 to 6 per cent., a discrepancy too great to be allowed in a case like this, it was given up. Determined then to revert again to oxide of lead, and to prepare a pure oxide myself, I took red lead (2PbO.PbO2), and dissolving out the protoxide with dilute nitric acid, washed well the resulting binoxide; this, by careful ignition over an air-flame, loses its extra oxygen-atom, and passes with incandescence to the state of protoxide. Working with oxide prepared in this manner, I obtained highly satisfactory results, and subsequently used this method only for the completion of the analyses in the table. By examining the gradation of the numbers on the table, it is seen that the percentage increases or decreases regularly accordingly as the specific gravity rises or falls, proving that the strength can be correctly deduced from a knowledge of its density, and that, unlike acetic acid, it presents no anomaly in this respect; also, that when a strong acid is diluted with water, though a considerable quantity of heat is evolved, no condensation in volume follows. The correctness of the numbers may be also somewhat checked in the following manner :-Take 100 fluid grains of 1.508 acid: this will weigh 150.8 grs., and contain 74.79 grs. by weight of PO5; dilute this with 100 fl. grs. of water: the whole will weigh 250-8 grs., and contain 74.79 grs. by weight of PO; each 100 parts by weight will be therefore of sp. gr. 1·254, and contain theoretically 29.7 parts by weight of acid; by referring to the latter sp. gr. on the table, we find by experiment such number to contain 29-16 per cent. Again, 100 fl. grs. of acid 1.285 sp. gr. will weigh 128.5 grs., and contain 41.03 grs. by weight of PO; diluted with 100 fl. grs. of water, it will weigh 228-5 grs., and contain 41·03 grs. of acid, being of sp. gr. 1.142; each 100 parts of acid of this sp. gr. should contain then 179 by weight of PO5. Reference to the table shows us 17.89 per cent. A great many numbers have been checked in this manner, and they were all found to be correct. The temperature at which all the specific gravities were taken was 15.5 C. (60° Fahr.). This is, of course, an important point in using the table, as the volume of liquid varies considerably according to the temperature; and as at different heights of the thermometer comparison of volumes no longer holds good, comparison of percentages would be equally fallacious. I may add that the acid used was prepared from common phosphorus in the ordinary manner; but I have since made several examples of acid from amorphous phosphorus, as first mentioned by Mr. Groves, and decidedly prefer this latter method; the phosphorus is readily acted upon, its use entails no danger, and a product is obtained in a few hours which ordinarily would take as many days. One little objection appeared, which is apt to make one think that the product is not absolutely pure, viz., that in the concentrated state it was more or less coloured, possessing a brownish or yellow tint; this might have arisen from the particular specimen of amorphous phosphorus operated on: probably another sample would not show this defect. XLVI.-Note on Messrs. Calvert and Johnson's paper (November, 1866, p. 434.) By A. MATTHIESSEN, F.R.S. "On the IN most of the tables given in this paper (Tables 6-12) there will be found a column headed "Loss calculated according to the composition of the alloys." The numbers given under this heading are, however, all faulty, as the authors have calculated these values from the weights of the metals composing the alloy, using the co-efficients, as they may be called, of the action of the acid on their surface as the co-efficients of the action of the acid on their weights; thus, in Table 7, p. 445, they give the following: 83.7 Now 100 grms. of the first alloy consist of = 11.7 c.c. 7.15 zinc (for 1 c.c. weighs 7·15 grms.) and 16.3 8.95 = 1.8 c.c. of copper (for 1 c.c. copper weighs 8.95 grms.); or 1 c.c. of the alloy consists of 0.86 c.c. zinc and 0·14 c.c. copper. The loss on 1 c.c. zinc by the action of hydrochloric acid being 0.200, on 0.86 c.c. it will be 0.172, and that of the acid on copper being 0-000, the calculated loss on 1 c.c. alloy is 0.172; or the calculated loss on the square meter, deduced from the composition of the alloy, will be 287, instead of 279, as given in the table. Similarly the calculated loss on the alloy ZnCu, will be 68 instead of 56.83. The authors' method of calculation is, as stated, the use of weight instead of surface; thus their calculated values are found by multiplying the weight-percentages by the co-efficients, and dividing by 100; for 837 x 3.3333 279; and 17.05 x 3.3333 = 56.83. |
