360 THE COLLIERY GUARDIAN. February 25, 1916. vapour by volume, and its oxygen percentage is 20-09. The unadjusted result of analysis would, therefore, in this case be 0-84 per cent, in error. However the matter may be viewed, the point of practical importance is the percentage which really exists in the air in its actual state. The lamp is graduated in such a way that it gives this actual oxygen percentage automatically, and without the need for correction. In order to make a comparison with the lamp read- ings, all analyses had, therefore, to be corrected for the presence of aqueous vapour. As Glaisher’s Tables did not have the necessary range, the writer was obliged to construct a table for his own purposes, and as this may be useful to others, it is given in Table I. The instructions for using the table are as follow :— Determine the percentage saturation of the air; note down the vapour pressure (column 2) given opposite the temperature corresponding to the dry-bulb reading; divide the vapour pressure by the barometer reading; Fig. 2. multiply the figure so obtained by the percentage satur- ation; the result is the percentage by volume of aqueous vapour present. The facte that hot air can absorb a greater proportion of aqueous vapour than cold air, and that aqueous vapour has a very pronounced action on a flame, supply reasons why the lamp tends to give continuously lower results as the temperature of the saturated air rises. The influ- ence in question is of no real importance until the temperature exceeds 70 degs. Fahr. Between 70 degs. and 85 degs. Fahr, the effect, although no longer negligible, does not assume ■ extreme proportions, and thus it has been possible approximately to allow for it by providing a second scale on which readings are to be taken when the temperature lies between these limits. As the temperature of the saturated air rises above 85 degs. Fahr., however, the influence of humidity becomes very striking. The following figures, although relating to air temperatures above those normally exist- ing in mines, are interesting in this connection. For contrast, the lamp readings were taken on the ordinary or low temperature scale. Humidity is indeed so dominant a factor in hot air that if the temperature were raised to a point which appears to lie between 130 degs. and 140 degs. Fahr, the lamp would refuse to burn at all in fresh saturated air. Table II.—Influence of Humidity on Lamp Headings. Barometer reading, 29'7 in. Hygrometer readings. Dry Wet bulb. bulb. Degs.F. Degs.F. igO ri E3 > Pm J s & P ® O 97’0 ... 97 ... 100 ... 5’90 ... 20'75 ... 19’53 ... 17'3 92’0 ... 92 ... 100 ... 5’04 ... 20'52 ... 19'49 ... 18'0 87'5 ... 86 ... 93 ... 4'08 ... 20'45 ... 19'62 ... 18'5 In the experiments, high temperatures were obtained by introducing pieces of red hot iron into the test chamber. These were made to boil water and so main- tain saturation. Accuracy of the Method. Numerous readings were taken at ordinary tempera- tures, to allow the precision of the method to be assessed; and the average error for the whole series of 152 determinations was found to be slightly under ± 0'24 per cent. An analysis of the errors revealed by these readings is as follows :— Magnitude of errors. Per cent Over ........ 0'7 Between 0'6 and 0'7 „ 0'5 „ 0'6 „ 0'4 „ 0'5 „ 0'3 „ 0'4 „ 0'2 „ 0'3 Under........ 0'2 Frequency of errors. Headings. Per cent. 1 in '52, or 0'7 3 „ 152, „ 1'9 8 „ 152, „ 5'3 14 „ 152, „ 9'2 29 „ 152, „ 19'1 27 „ 152, „ 17'8 70 „ 152, „ 46'0 The accuracy of the high-temperature scale was also tested by a considerable number of readings, which went to show that it gives values, automatically corrected for water vapour, with much the same order of precision as the first or low-temperature scale. Underground Tests. Through the kindness of Mr. Hugh Waddell, the writer was able to make a useful set of underground tests in the Four-foot seam at St. Germains Colliery, in workings which have been temporarily abandoned. Those trials indicating least oxygen were made in a stone mine in which the air was stagnant. The lower part of this mine was full of blackdamp. A sample was taken during each trial, and afterwards analysed. In order to correct the analyses for water vapour, hygro- metric readings were also booked. Determinations with the Haldane tube were made at most of the pointe. Mr. Waddell took the majority of the latter readings, his value occasionally being checked by others present. The average error of the lamp readings was ± 0'19 per cent. The device appears to give more satisfactory results in the pit than in the laboratory, possibly because in the larger volumes of the pit the air is not being changed appreciably by the products of combustion of the lamp itself, and therefore is less subject to fluctuation in quality during an experiment. Influence of Variations in the Composition of Blackdamp. As is now well known, the blackdamp of mines con- sists principally of nitrogen. The ratio between nitrogen and carbon dioxide is very variable, and it was necessary to ascertain whether this variability would have any influence of importance on the readings given by the lamp. The device was graduated and tested in air polluted with blackdamp of the composition N : CO2 : : 7'67 : 1. A series of observations were taken in air containing various percentages of pure nitrogen, and analyses were made of every sample of air. No distinction whatever could be drawn between blackdamp of pure nitrogen and the blackdamp used in the original calibration. Any difference which might exist in the effects on the lamp of these two kinds of blackdamp is certainly considerably less than the experimental error. The effect of pure carbon dioxide was next investi- gated; and this proved more marked, the lamp giving low readings (difference nil to 1'15). Blackdamp consisting solely of carbon dioxide is unknown in British mines, but these results assist us to judge the size of correction required when the lamp is used in air containing blackdamp richer than usual in carbon dioxide. The composition of the blackdamp in British mines varies between almost pure nitrogen and one bearing almost 50 per cent, of carbon dioxide. No correction whatever needs to be applied to the lamp readings with blackdamp, the carbon dioxide proportions of which range between zero and 25 per cent, (and this range < ’.. *■ "fa w*- ^4? ? • •*K.- ‘ X. Fig. 3. includes the vast majority); when the carbon dioxide proportion rises to 40 per cent., the lamp reads 19 instead of 19'28; when the proportion reaches 50 per cent., the 19 mark is 0-35 per cent, in error. Except in very extreme cases, therefore, alteration in ■the composition of the blackdamp present has a negligible influence on the lamp values. Influence of Firedamp. Since the device is intended for use in safety lamp mines, the possible interference of firedamp cannot be overlooked. A number of experiments were carried out with the lamp in a long, narrow box, through which was made to flow a steady current of air containing various proportions of blackdamp and percentages of inflam- mable gas (coal gas) ranging from zero to 2|. Samples were taken in the usual way, withdrawn and analysed. The results were unexpected, the inflammable gas causing the lamp to give high readings. The lamp, in fact, disregards entirely the presence of the gas, and treats it as though it were so much air. For example, in saturated air containing a little firedamp and no blackdamp, the lamp gives the oxygen value for perfectly fresh saturated air. This effect is barely noticeable when the firedamp proportion is below that unmistakably discernible on the lowered flame of the lamp (that is, below about 1J per cent.), and can then be disregarded. But with firedamp percentages between 1| and 2|, the gas must first be estimated by means of the “ cap,” and then one-fifth of its value deducted from the lamp reading for oxygen, in order to correct the latter for its presence. The following series of results (Table III.) is selected from several similar sets :— Table III.—Air Contaminated with both Blackdamp and Inflammable Gas. Mean temperature, 48 degs. Fahr. Mean relative humidity, 90 per cent. ( Created for aqueous vapour. Error of lamp- reading before correction Lamp- reading Error of lamp- reading after correction. ( Inflam- mable gas. Per cent. reading. Oxygen. Percent. Percent. J inflam- mable gas. 2'47 .. 18'85 . . 19'50 .. +0'65 . . 19'0 .. +0T5 2'23 .. 18'68 . . 19'25 .. +0'57 . . 18'8 .. + 0'12 1'98 .. 18'80 . . 19'15 .. +0'35 . . 18'75 .. -0'05 1'73 .. 18'68 . . 18'95 .. +0'27 . . 18'6 . -0'08 1'48 .. 18'80 . . 19'0 .. +0'20 . . 18'7 .. -OTO 1'24 .. J8'90 . . 18'95 .. +0'95 . . 18'7 .. -0'20 0'99 .. 18'96 ... 19 05 ... +0'09 ... 18'85 Extension of the Method. .. —O'll This method of determining the oxygen percentage is not limited to proportions between 16'5 and 21, although that range is probably sufficient for every-day purposes. The first model, for instance, was graduated up to 35 per eent. of oxygen; while, if the hydrogen flame were employed, as in the Clowes lamp, the range of the readings could be extended in the other direction to the neighbourhood of 9 per cent. COLLIERY RECRUITING COURTS. The Home Secretary announces, under date February 18, that he has had under consideration, in consultation with the War Office, the question of the .arrangements to be made for dealing with applica- tions for exemption from military service in respect of men employed at the central rescue stations established for the purposes of the Coal Mines Act, 1911. The provisions of the Military Service Act, 1916, apply to all men employed at such stations who are not already ■attested, and who fall within the description in section 1 of the Act; but the Home Office has certified, in pur- suance of section 2 (2) (which provides for the issue of certificates of exemption) that the work of men belong- ing to a permanent rescue corps maintained at a central rescue station established for the purposes of the Coal Mines Act, 1911, or to the technical staff of such stations, is work of national importance. It has been arranged that all applications for exemption from mili- tary service of such men, whether attested under Lord Derby’s scheme or coming under the Military Service Act, shall be dealt with by the Colliery Recruiting Courts in accordance with the supplemental instruc- tions. (See below.) For this purpose, it will be necessary that the authority controlling the station should make out, on forms supplied for that purpose, lists of all men of military age employed at the station, and coming within the classes defined above. The list of men to whom the Military Service Act applies should be made out on Form 5, and the list of attested men on Form 6. Two copies of each list should be sent, duly certified, to the Divisional Inspector of Mines before March 2, and one copy of each list should be retained at the station. All the applications in respect of a central rescue station will be taken at the same hearing, and due notice will be given by the Colliery Recruiting Courts of the day on which the hearing will take place. N.B.—The penalty for making a false statement or representation for the purpose of obtaining exemption for oneself or for any other person is six months’ imprisonment. Supplemental Instructions with Regard to Men Employed at Colliery Rescue Stations. (1) The Home Office has certified that the work of men belonging to a permanent rescue corps maintained at a central rescue station established for the purposes of the Coal Mines Act, 1911, or to the technical staff of such stations, is work of national importance. (2) It has been arranged that the question of the exemption from military service of such men, whether attested under Lord Derby’s scheme or coming under the Military Service Act, shall be dealt with by the Colliery Recruiting Courts. (3) The authorities of the stations have been requested to forward to the Colliery Recruiting Court (in duplicate) before March 2, 1916, the names and other particulars of the men belonging to the permanent rescue corps (if any) of the station and to the technical staff, who have attested or to whom the Military Service Act applies. (4) The Court will forward the duplicate copies of the forms received from a central rescue station to the military representative, and will proceed to deal with the applications, following as near as may be the pro- cedure laid down in the general instructions for coal mines. If the Court, after hearing the parties, are satisfied that a man is a member of a permanent rescue corps or of the technical staff of the station, and that his services are indispensable to the work of the station, they will grant him a certificate of exemption (Forms A and B for coal miners may be used with the necessary adaptation). The Adjustable Cover and Boiler Block Company Limited have applied for the restoration of the patent granted to John Robert Hannan for an invention relating to side flues and downtakes for boilers (numbered 6831 of 1911), which expired on March 18 last, owing to non-payment of renewal fee.