866.30 89.8

4.70 24.64 864.10

90.10 4.67

24.70

ON SOURCES OF ERROR IN DETERMINATION OF NITROGEN BY SODALIME, AND MEANS FOR AVOIDING THEM.

By W. O. ATWATER.

(Continued from page 18.)

Five series of trials were made. Previous experience had persuaded us that when (1) the tubes are of moderate length and compactly filled with soda-lime, (2) only a moderately high heat is used, (3) the combustion does not proceed too slowly, and (4) the flames are turned off and the tube allowed to cool slightly before aspirating with air, there is no considerable loss of nitrogen by either dissociation or oxidation. In the first series, in which the operation was conducted in the usual way, a confirmation of this impression was sought. In the second series the effect of increasing the length of the tube and with it the time of sojourn of the ammonia gas in the tubes, without increasing the heat, was observed. In the third series the effect of high heat was tested by using long tubes as in the second series, and making the heat much greater. In the fourth series it was sought to learn whether the loss of nitrogen observed in the third series was due to dissociation or oxidation or to both. The trials of the fifth series had a similar object. The results are given in detail in Table II., which includes all the deter minations made, and are recapitulated in Table III.

The figures of the first series indicate that with tubes of our ordinary length, 40 cm. or a little less, compactly filled (about 16 cm. with mixture of fine soda-lime and substance, 4 cm. with "rinsings" of fine soda-lime, and 12 cm. with an anterior layer of coarse soda-lime), at a heat sufficient to make the tube dull red, designated here as "medium," and with aspiration by air after the tubes had begun to cool, there was no loss of nitrogen. In the second series the tubes were long enough to make the anterior layer of coarse soda-lime about 35-40 cm. ; the charging otherwise was the same as in the first series. The percentage of nitrogen obtained was the same. Lengthening the tube had no effect upon the result. At moderate heat there was no loss by dissociation with closelyTABLE III.

Recapitulation of Determinations of Nitrogen in Ammonium Sulphate under Different

Conditions.

packed tubes, even when the latter were very long and the exposure of the ammonia

to the heat was increased.

* Tube about 40 c.m., anterior layer of soda-lime about 12 c.m.

Tube 75 c.m., anterior layer about 35-40 c.m.

In one case with carbonic acid.

In the third series the conditions were the same as in the second, except that the temperature was made as high as the tubes of the most difficultly fusible Bohemian glass we could obtain would endure without bursting. The standard acid employed was rather concentrated, so that but a small quantity was needed in the nitrogen bulb, and the internal pressure was thus reduced to a minimum. It was thus possible to heat the tubes to bright redness without their bulging. Instead of 21.12, only 20.83 per cent. of nitrogen was obtained. This falls short of the actual amount by 0.29 per cent. of the weight of the sulphate of ammonia, or 1-4 per cent. of the total nitrogen. The indication of loss by either decomposition or oxidation of ammonia was very apparent.

In the fourth series the conditions were the same as in the third, except that air was excluded, the object being to find, if practicable, how much of the loss in the previous series was due to the burning of ammonia by the oxygen of the air, and how much to dissociation. In No. 10, the length of the tube was actually 80 cm. instead of 75 cm. as in the other cases. The extra 5 cm. of the posterior end were filled with bicarbonate of soda, which was heated at the beginning of the experiment to expel the air present in the tube, and again at the end to drive out the residual ammonia. In Nos. 11 to 14, as in all of the next series, in which hydrogen was used for the same purpose, the tubes were about 80 cm. long or a little longer, the extra 5 cm. at the posterior end being filled with asbestos. The hydrogen, which had been dried by sulphuric acid, was passed through the combustion tube for three quarters of an hour, and the tube was then exhausted by a mercury pump, after which hydrogen was again passed through for half an hour. Assuming that the air had thus been very nearly all removed, the combustion was conducted at the very high heat, as in the third series. When it was done, hydrogen was again passed through to wash out the residual gases, precautions being taken to admit no air. The amount of nitrogen obtained averaged the same as in the third series, 20.83 per cent. The exclusion of air made then no difference in the result. This indicated that the loss was due not to oxidation, but to dissociation of ammonia.

It is observable, furthermore, that the individual results in the third and fourth series vary considerably, the range in the fourth series being 21, while in the first and second series it was only 03 per cent. While the agreement of duplicates is a very uncertain evidence of the correctness of an analysis, a wide disagreement may be regarded as a tolerably sure indication of error.

In the fifth series the conditions were the same as in the fourth, except that the combustion was made at "medium" heat. The results, which average 21.11 per cent., are practically identical with each other and with those of the first and second series. The difference in condition between this and the fourth series, like that between the second and third, is simply one of heat, and that difference in each case evidently makes the whole of the difference in result.

To resume :-In every case in which the medium heat was employed, whether with long or with short tubes, whether with or without air, the full amount of nitrogen was obtained. In every case with the high heat there was a loss from 1 to 2 per cent. of the total nitrogen in the substance. Neither the length of the tubes nor the presence or absence of air made any difference in either the amount of nitrogen obtained or the uniformity of the results, but the high heat materially reduced the amount of nitrogen and made wide variations in results of duplicate determinations.

*

That more definite statements as to temperature at which the dissociation takes place are to be desired, goes without saying. Ramsay and Young, in a series of very interesting experiments on the temperature of dissociation of ammonia, find that the point at which it commences varies greatly with the nature of the surrounding medium.

*Jour. Chem. Soc., 1884, Proc. p. 88.

In a porcelain tube filled with broken pieces of porcelain, in an iron tube filled with porcelain, and in a glass tube filled with ignited "porous " asbestos cardboard, to expose the gas to a large surface, the decomposition commenced at about 500° or below. At 500°-520°, however, it was very small, but increased gradually at higher temperatures. In contact with a glass surface the temperature at which decomposition begins was much higher. The nature of the surface heated has a very great influence on the amount of ammonia decomposed. In a plain dry iron tube the decomposition was apparently complete at 780°, but if water was present only 95 per cent. was decomposed. At 760°, in a glass tube containing iron wire, 64-3-76 per cent. of the ammonia was decomposed; but when copper was substituted (the other conditions remaining essentially unaltered) only 2.0 per cent. was decomposed. The authors find that "the amount of decomposition depends partly upon the rate of passage of the gas, or, in other words, on the time of exposure to heat," and that "the extent of surface also influences the amount of decomposition.

(To be continued.)

LAW NOTES.

HEAVY PENALTY FOR ADULTERATED MILK.-At Wolverhampton Police Court on January 30th, before Mr. Neville (stipendiary)-F. W. Vickers, Tissington, Ashbourne, Derbyshire, was charged with selling adulterated milk.-Mr. Brevitt (town clerk) prosecuted, and said that the difficulty the prosecution had had in this case was to secure the person who, under the Act, was really liable for the alleged adulteration, and, if the defendant were convicted, he must ask for a substantial penalty.Inspector Blanton deposed that on January 2nd, from information received, he went to the London and North-Western Railway station at Wolverhampton, and saw a churn of milk containing twelve gallons. It bore a warranty label, and was consigned from Ashbourne to the Midland Dairy Company, Horseley Fields. Witness took a sample from the churn, and had it analysed by Mr. E. W. T. Jones. the borough analyst, who certified that it contained 19 per cent. of water.-Mr. Paine, for the defence, urged that the defendant had received no notice from the prosecution of their intention to test the milk, nor had he received a sample from them.-The Stipendiary said he thought it would be fairer to the defendant in future if a sample were supplied to him after it had been taken by the prosecution, although there was no legal obligation upon them to do so. It was satisfactory that the original vendor of the milk had been found and proceeded against. In justice to the milksellers in the town, he must impose the full penalty under the Act-namely, £20, and costs.

ADULTERATED PEPPER.-At Glasgow Sheriff Court on the 14th ult. Matthew Kerr, grocer and provision merchant, 61A, King Street, Calton, was charged before Sheriff Balfour, at the instance of Mr. Peter Fyfe, sanitary inspector, with having, on 19th December, sold to Mr. Robert Inglis, assistant sanitary inspector, a quarter pound of black pepper, which on analysis was found to contain 3 per cent. of sand, 4 per cent. of mineral matter, and 7 per cent. of pepper husk, all of which are extraneous to whole pepper. The respondent pleaded guilty. His agent, Mr. Wm. Shaw, writer, stated that Mr. Kerr bought the pepper from a house in Glasgow which held a guarantee from a Liverpool house that the pepper was pure. It was what was known as Penang pepper, which had naturally a large amount of impurity in it. After hearing a further statement from Mr. Shaw, Mr. R. G. Ross, writer, who prosecuted, and Dr. Tatlock, the analyst, his Lordship gave judgment. The Sheriff said that he thought Mr. Kerr had been well advised in tendering a plea of guilty. It appeared that black pepper had got a core and an outside husk, and in preparing it for the market there must be to a greater or a lesser extent a certain quantity of sand and mineral matter adhering to the pepper. Dr. Tatlock had taken the Somerset House standard, which allowed a percentage of 3 of sand, and in regard to mineral matter he had been guided by public analysts and writers of authority, who allowed 7 per cent. for mineral matters, and as long as the percentage of sand and mineral matter only came to 3 and 7, no prosecution would be directed against any party who sold black pepper. But the line must be drawn somewhere. From the manner in which this black pepper was prepared, it was perfectly clear that the pepper berries, after being dried, must have particles of earthy matter adhering to the husks, and if black pepper were sent over to this country with an immense proportion of earthy matter adhering to the husks, with the intention of being sold in that way, it would not do to allow such a sale to take place, because the earthy mattter might get in, not by fair, but by foul means. To prevent that the Somerset House and those public analysts and writers of authority had fixed what he presumed were reasonable and fair standards. Dr. Tatlock had acted most liberally in stating the adulteration, because, in point of fact, the mineral matter really amounted to about 16 per cent., and the sand to about 6 per cent. It was not to be supposed that in inflicting a light penalty, as he was going to do, he by any means countenanced black pepper being sold in the state in which Mr. Kerr had sold it. But he had no reason to doubt Mr. Kerr's bona fides in the matter. He apparently bought from a wholesale house, who, on their part, held a written guarantee from the foreign sellers. Mr. Kerr, unfortunately, had not been armed with such a written guarantee, and he was therefore liable to the authorities for selling the adulterated article. As it was the first case of the kind that had been brought before him, the Sheriff, in the circumstances, inflicted a penalty of 158. The fine was paid,

CORRESPONDENCE.

[The Editor is not in any way responsible for opinions expressed by his correspondents.]

To the Editor of the ANALYST.

SIR,-As few penalties for adulteration are inflicted, the enclosed report* may interest your readers, especially as the case comes under the special provision of the Act for procuring milk for analysis at the railway station, or in course of delivery. The following are the analytical results of this sample of milk:

SIR,-Now that the Society of Public Analysts have appointed a Select Committee (which for brevity's sake we shall term the A B C of the Society) to investigate the subject of Butter Analysis owing to the supposed alarming state of matters brought about by Mr. Allen's late paper, entitled "Abnormal Samples of Butter," it may be of interest to the members of the A B C to know that as far back as the year 1884, Professor Wiley of Washington, in analysing nine samples of genuine butter found as a minimum for insoluble fatty acids 88.50, and a maximum of 89.89 per cent., the first figure being Angell and Hehner's highest figure.

In the year 1886, Professor E. Waller, of New York, found 90-26 per cent. as a maximum, and 86 40 as a minimum for twenty-six genuine butters examined by him; and in the same year Professor C. B. Cochrin found 87.7 per cent, as his highest figure, and 86 7 as his lowest figure in twenty-five genuine Pennsylvania butters, figures which prove conclusively that it is not only in Danish Butters that high percentages of insoluble fatty acids are to be found. The figure 89-89 is as near as a toucher to 90 per cent. (and we all know what as near as a toucher means), a figure obtained in the year 1884, the difference between 89.89 and 90 being less than the difference between the figures obtained by Mr. Allen in his two analyses which were performed in duplicate, and by a strange coincidence Professor Waller's highest figure 90-24 obtained in 1886 coincides with one of Mr. Allen's estimations. Is it possible that the A B C are ignorant of these facts ?-Yours, etc.,

THE GREAT I AM.

F.A. B.-Had you applied some years ago you might possibly have gained admittance without exam. ination, but, so far as we know, such days are now over. We are not aware that there is any relaxation of the rule as to the fixed course of study, and, moreover, we fear that, even if there were, the examination itself would present an insuperable barrier to a man in business who had not time to go through a special course. That this should be so is only just, because it is intended to exclude all but those who really make an actual profession of chemistry as distinct from pharmacy. Undoubtedly some pharmacists have managed to get in at present, but, as they die off, their places are not likely to be filled up by others of the same status, because a man who became a practising consulting chemist would naturally drop the shop altogether, it being impossible to combine the two businesses, which are totally distinct in every respect.

PROF. KINNICUTT.-Letter to hand but no paper arrived yet (February 25th). When it comes will make use of it as soon as possible.

Communications on Literary or Exchange Matters to be sent to 325, Kennington Road, London, S.E.

*See Law Notes.