EGGERTZ gives in his Swedish work, "Om Kemisk, I grm. of the iron specimen is dissolved in 12 c.c. of nitric acid; the liquor is next evaporated on a sand-bath to dryness; the residue is dissolved in 5 c.c. of aqua regia, and to the solution 4 c.c. of water is added. The liquor is filtered from the silica; the filtrate must not be more than 20 c.c. From this solution the phosphorus is precipitated by about 30 c.c. of molybdic liquor, the preparation of which has been already mentioned. The solution is left for 15 hours in a warm place, and is then filtered. The precipitate containing phosphorus is washed by cold water acidulated with one per cent. of nitric acid. The yellow precipitate is dried on the filter at 100° in an air-bath and weighed. This precipitate contains 1·63 per cent. of phosphorus. On this process I wish to make some remarks-practical remarks, I had better say. 1. For dissolving iron it is better to use aqua regia, because nitric acid is not such a powerful agent for decomposing the whole of the organic matter which is often found in irons; the presence of this was found to prevent the precipitation of phosphorus by the molybdic solution. 2. The process of filtration and washing of the yellow precipitate must be executed very rapidly, because otherwise a certain quantity of the yellow precipitate is dissolved, and passes through the filter with the solution. Many trials were made, and it was always found that a small quantity of the precipitate passed into solution. In this case a lower percentage of phosphorus is obtained; this gives incorrect results in analysing steels and irons, and such materials where a small amount of phosphorus not estimated may give faulty results in the classification of the materials. 3. Eggertz advises to wash the yellow precipitate with water acidulated by nitric acid, and dry it on the filter at 100°. In practice this operation is nearly impossible, firstly because the precipitate is slightly soluble in acidulated water, secondly because a small quantity of the acid always remains on the filter, from which the filter when dried is always a little rotten; this fact also influences the percentage of phosphorus calculated. The best method was found to be the following: I grm. of the specimen is dissolved in 20 c.c. of aqua regia, and the phosphorus is precipitated by Eggertz's the solution, is dissolved on the filter in ammonia, and in method; the resulting yellow precipitate, separated from the filtrate obtained, slightly acidulated by hydrochloric acid, the phosphorus is precipitated in the form of phospho-ammonio magnesic salt [Mg(NH4)PO4] by "magnesium mixture," prepared by dissolving 1 grm. of MgSO4 and 1 grm. of NH4Cl in 8 c.c. of water mixed with 4 c.c. of ammonia. The precipitation is finished in 15 to 20 hours; the precipitate is filtered from the solution, washed with water containing half a per cent. of ammonia, and first gently heated in a platinum crucible till free NH3 and H2O are evaporated; the crucible next is ignited for 30 to 40 minutes, and the received This salt contains 13.51 per cent. Mg2P2O7 is weighed. of phosphorus. This combination of Eggertz's method with the old one gives very exact results in analyses of irons and steels. Obouchoff Steel Works, St. Petersburg. NEW APPLICATIONS OF GLYCERIN IN THE By A. H. CHURCH, M.A. FOR some time past I have used glycerin for preventing the adhesion of vulcanised india-rubber tubing to the inlet pipes of Bunsen and other gas-burners. A drop or two smeared on the parts in contact prevents both surfaces from suffering those changes which give rise to such continued annoyance in the laboratory. The glycerin should be pure. One of the most serious drawbacks to the use of paraffin lamps for microscopic and other purposes is the perpetual creeping out of some of the hydrocarbon through the cement wherewith the metal burner is fixed to the glass reservoir. If this cement be soaked with glycerin before oil of any kind be introduced into the lamp this annoyance does not occur. ON THE SPECTRA OF LIGHTNING. By J. W. CLARK. ANOTHER Opportunity of observing the spectrum of forked lightning having occurred, the following observations were made: Out of 26 observations, II spectra showed bright lines of oxygen, nitrogen (at times apparently also of hydrogen), 7 more were uncertain on account of their being too faint, and the remaining 8 were continuous, but without lines. A few more spectra resembled those previously described (CHEMICAL NEWS, vols. xxx. and xxxii.), in which parts of the spectra were alone visible, particularly the red end, but sometimes the space between the solar lines D and F or D and E was seen of a uniform and almost white colour (CHEMICAL NEWS, vol. xxxii.), which now seemed to be possibly due either to the flash not being sufficiently bright or to its not being in the direction of the axis of the spectroscope. Previously, however, the same appearance was observed with very bright flashes. The density of the air in which the discharge takes place will probably influence the nature of the spectrum, and the amount of aqueous vapour may also affect it, as determining the amount of incandescent hydrogen, which, as is well known, shows remarkable changes in its spectrum when subjected to varying pressure and temperature.* THE ANALYSIS OF SOAP. Weighing. In all methods usually given in text-books the analyst is directed to weigh out for each operation small portions (1 to 5 grm.) of the sample. This plan is to be avoided, and for two reasons:-(1) Soap is extremely variable in composition, and considerable variations are possible even in the same sample; (2) It is perpetually losing water by evaporation from its surface. As the soap is usually weighed in the form of thin shavings, the surface exposed is, in relation to the weight taken, very considerable. These two sources of inaccuracy are obviated by weighing out for the analysis a section cut through the bar at right angles to its length (60 to 80 grms.), dissolving in distilled water, and making the volume up to 1000 c.c. (in the cold); 50 c.c. of this solution are measured off for each operation. It should be observed that as some of the alkaline salts of the fatty acids separate out from the solution on cooling it must be well mixed, by agitation, previously to drawing off each 50 c.c. The several operations are conducted as follows: I. Total Alkali.-50 c.c. of the solution are diluted to about 200 c.c., the liquid is coloured faintly with eosine, and standard acid is run in, taking care to stir briskly with a glass rod. The neutral point is extremely well marked by the sudden decolorisation of the whole. The cause of this apparent destruction of colour is the union of the fatty acids with the eosine at the moment of their complete separation from the fluid. II. Uncombined Alkali,-50 c.c. are added to 300 c.c. of a saturated solution of common salt, which must be, of course, neutral to test paper, and the volume made up to 400 c.c. The neutral alkaline salts of the fatty acids (i.e., true soap) are precipitated; any excess of alkali present remains in solution; this is determined in an aliquot part of the filtered solution; the filter must not be moistened previous to filtration; from this the total uncombined alkali is calculated, and subtracted from the total alkali already found. Then the combined and uncombined alkali are determined. III. Fatty Acids.-50 c.c. of this solution are introduced into a stoppered separating funnel, decomposed with excess of acid and agitated with carbon disulphide until * See Wüllner, "Lehrbuch der Physik," Bd. II., s. 244, and Schellen "Spectralanalyse," s. 167. the liberated fatty acids are dissolved. The disulphide solution of the fats is drawn off into a tared flask; the aqueous solution is washed once or twice with small portions of disulphide, the whole of which is then separated from the fats by distillation. The fats are purified from the last traces of CS2 by heating the flask for a short time at 100° C.; the weight, after cooling, less the tare, gives the weight of the fatty acids. Ordinary ether may be used in place of the CS2; it has, however, the disadvantage of retaining small quantities of water, and, therefore, aqueous acids, which must be driven off at the end of the operation by exposing to a temperature of 100 to 120° C., until the weight is constant. Further, the ethereal solution will be the upper stratum, and is, for obvious reasons, not so easily to be manipulated as the bisulphide solution, which forms the lower layer. Note. A moment's consideration of the following equation representing the decomposition of sodic oleate by HC1: 2 (C18H330. Na 2NaCl + 2C18H330 8H330>0. >O + 2HC1 = will make it evident that while the fatty acid is present in the soap in the form of anhydride, it is separated and weighed in the course of analysis as hydrate. A correction must, therefore, be applied based upon the fact that 282 parts oleic hydrate = 273 parts oleic anhydride-i.e., the weight of the fatty acids is to be multiplied by the decimal fraction o‘97. In the case of the "Olein" soaps of commerce a very rapid and tolerably accurate estimation may be made in the following way:-50 c.c. of the solution are decomposed with HCl in a small flask, the neck of which is long and narrow, and graduated in c.c., and so much water added that, upon heating in the water-bath, the separated oil will rise into the neck and fall entirely within the graduated portion. The heating must be continued, with occasional tapping of the flask, until the whole of the fat has been separated and has risen into the neck. The flask is allowed to cool, and when cool the volume of the oil is read off. This quantity, multiplied by the specific gravity of the oil, gives its weight. The specific gravity (which I have almost always found to be o'g) may be determined by pouring off a small quantity into a capsule; (a second reading will give the volume taken), and weighing it; the weight divided by the volume is the required specific gravity. IV. Water. If the purity of the sample has been ascertained this constituent may be calculated by dif ference. The direct estimation is effected by evaporating 50 c.c. of the solution to dryness on the water-bath (finally in the air-bath from 100° to 120° c.) in a weighed dish. The residue is anhydrous soap; from its weight the percentage of water in the soap may readily be calculated. It may be observed that the usual method, which consists in the exposure of the soap, previously cut into thin shavings and weighed, to the temperature of boiling water until it ceases to lose weight, is inaccurate, as it fails to drive off the last portions of water (1 to 2 per cent), which seem to have contracted a stronger union with the soap. V. Mineral impurities and unsaponified fat may be detected by taking the dried soap from the preceding operation, dissolving in strong alcohol, and filtering through a funnel heated by means of a jacket of hot water. Mineral impurities remain upon the filter as an insoluble residue, the weight of which is readily ascertained. The alcoholic filtrate is evaporated with successive additions of distilled water; by these means any unsaponified fat or resin is separated from the soap, which, of course, remains in aqueous solution. This solution may be used for I., II., or III. The mineral impurities may be examined qualitatively after drying and weighing. The Laboratory, Owens College, December 15, 1876. C. F. C. |