Hammerschmidt has calculated a similar table for the correction of volumes of gas measured at temperatures ranging from 0° to 30° C., and under pressures from 660 to 780 mm., to 15° C. and 760 mm. It is based on the coefficient of expansion of acetylene given in Chapter VI., but, as was there pointed out, this coefficient differs by so little from that of the permanent gases for which the annexed table was compiled, that no appreciable error results from the use of the latter for acetylene also. A table similar to the annexed but of more extended range is given in the "Notification of the Gas Referees," and in the text-book on "Gas Manufacture" by one of the authors.
The determination of the amounts of other gases in crude or purified acetylene is for the most part carried out by the methods in vogue for the analysis of coal-gas and other illuminating gases, or by slight modifications of them. For an account of these methods the textbook on "Gas Manufacture" by one of the authors may be consulted. For instance, two of the three principal impurities in acetylene, viz., ammonia and sulphuretted hydrogen, may be detected and estimated in that gas in the same manner as in coal gas. The detection and estimation of phosphine are, however, analytical operations peculiar to acetylene among common illuminating gases, and they must therefore be referred to.
Table to facilitate the Correction of the Volume of Gas at different Temperatures and under different Atmospheric Pressures.
_____________________________________________________
| | |
| | THERMOMETER. |
| BAR.|_______________________________________________|
| | | | | | | |
| | 46° | 48° | 50° | 52° | 54° | 56° |
|_____|_______|_______|_______|_______|_______|_______|
| | | | | | | |
|28.4 | 0.979 | 0.974 | 0.970 | 0.965 | 0.960 | 0.955 |
|28.5 | 0.983 | 0.978 | 0.973 | 0.968 | 0.964 | 0.959 |
|28.6 | 0.986 | 0.981 | 0.977 | 0.972 | 0.967 | 0.962 |
|28.7 | 0.990 | 0.985 | 0.980 | 0.975 | 0.970 | 0.966 |
|28.8 | 0.993 | 0.988 | 0.984 | 0.979 | 0.974 | 0.969 |
|28.9 | 0.997 | 0.992 | 0.987 | 0.982 | 0.977 | 0.973 |
|29.0 | 1.000 | 0.995 | 0.990 | 0.986 | 0.981 | 0.976 |
|29.1 | 1.004 | 0.999 | 0.994 | 0.989 | 0.984 | 0.979 |
|29.2 | 1.007 | 1.002 | 0.997 | 0.992 | 0.988 | 0.982 |
|29.3 | 1.011 | 1.005 | 1.001 | 0.996 | 0.991 | 0.986 |
|29.4 | 1.014 | 1.009 | 1.004 | 0.999 | 0.995 | 0.990 |
|29.5 | 1.018 | 1.013 | 1.008 | 1.003 | 0.998 | 0.993 |
|29.6 | 1.021 | 1.016 | 1.011 | 1.006 | 1.001 | 0.996 |
|29.7 | 1.025 | 1.019 | 1.015 | 1.010 | 1.005 | 1.000 |
|29.8 | 1.028 | 1.023 | 1.018 | 1.013 | 1.008 | 1.003 |
|29.9 | 1.031 | 1.026 | 1.022 | 1.017 | 1.012 | 1.007 |
|30.0 | 1.035 | 1.030 | 1.025 | 1.020 | 1.015 | 1.010 |
|30.1 | 1.038 | 1.033 | 1.029 | 1.024 | 1.019 | 1.014 |
|30.2 | 1.042 | 1.037 | 1.032 | 1.027 | 1.022 | 1.017 |
|30.3 | 1.045 | 1.040 | 1.036 | 1.030 | 1.025 | 1.020 |
|30.4 | 1.049 | 1.044 | 1.039 | 1.034 | 1.029 | 1.024 |
|30.5 | 1.052 | 1.047 | 1.042 | 1.037 | 1.032 | 1.027 |
|_____|_______|_______|_______|_______|_______|_______|
_____________________________________________________
| | |
| | THERMOMETER. |
| BAR.|_______________________________________________|
| | | | | | | |
| | 58° | 60° | 62° | 64° | 66° | 68° |
|_____|_______|_______|_______|_______|_______|_______|
| | | | | | | |
|28.5 | 0.954 | 0.949 | 0.944 | 0.939 | 0.934 | 0.929 |
|28.6 | 0.958 | 0.953 | 0.947 | 0.943 | 0.938 | 0.932 |
|28.7 | 0.961 | 0.956 | 0.951 | 0.946 | 0.941 | 0.936 |
|28.8 | 0.964 | 0.959 | 0.954 | 0.949 | 0.944 | 0.939 |
|28.9 | 0.968 | 0.963 | 0.958 | 0.953 | 0.948 | 0.942 |
|29.0 | 0.971 | 0.966 | 0.961 | 0.956 | 0.951 | 0.946 |
|29.1 | 0.975 | 0.969 | 0.964 | 0.959 | 0.954 | 0.949 |
|29.2 | 0.978 | 0.973 | 0.968 | 0.963 | 0.958 | 0.952 |
|29.3 | 0.981 | 0.976 | 0.971 | 0.966 | 0.961 | 0.956 |
|29.4 | 0.985 | 0.980 | 0.975 | 0.969 | 0.964 | 0.959 |
|29.5 | 0.988 | 0.983 | 0.978 | 0.973 | 0.968 | 0.962 |
|29.6 | 0.992 | 0.986 | 0.981 | 0.976 | 0.971 | 0.966 |
|29.7 | 0.995 | 0.990 | 0.985 | 0.980 | 0.974 | 0.969 |
|29.8 | 0.998 | 0.993 | 0.988 | 0.983 | 0.978 | 0.972 |
|29.9 | 1.002 | 0.997 | 0.991 | 0.986 | 0.981 | 0.976 |
|30.0 | 1.005 | 1.000 | 0.995 | 0.990 | 0.985 | 0.979 |
|30.1 | 1.009 | 1.003 | 0.998 | 0.993 | 0.988 | 0.983 |
|30.2 | 1.012 | 1.007 | 1.002 | 0.996 | 0.991 | 0.986 |
|30.3 | 1.015 | 1.010 | 1.005 | 1.000 | 0.995 | 0.989 |
|30.4 | 1.019 | 1.014 | 1.008 | 1.003 | 0.998 | 0.993 |
|30.5 | 1.022 | 1.017 | 1.012 | 1.006 | 1.001 | 0.996 |
|_____|_______|_______|_______|_______|_______|_______|
_____________________________________________
| | |
| | THERMOMETER. |
| BAR.|_______________________________________|
| | | | | | |
| | 70° | 72° | 74° | 76° | 78° |
|_____|_______|_______|_______|_______|_______|
| | | | | | |
|28.4 | 0.921 | 0.915 | 0.910 | 0.905 | 0.900 |
|28.5 | 0.924 | 0.919 | 0.914 | 0.908 | 0.903 |
|28.6 | 0.927 | 0.922 | 0.917 | 0.912 | 0.906 |
|28.7 | 0.931 | 0.925 | 0.920 | 0.915 | 0.909 |
|28.8 | 0.934 | 0.929 | 0.924 | 0.918 | 0.913 |
|28.9 | 0.937 | 0.932 | 0.927 | 0.921 | 0.916 |
|29.0 | 0.941 | 0.935 | 0.930 | 0.925 | 0.919 |
|29.1 | 0.944 | 0.939 | 0.933 | 0.928 | 0.923 |
|29.2 | 0.947 | 0.942 | 0.937 | 0.931 | 0.926 |
|29.3 | 0.950 | 0.945 | 0.940 | 0.935 | 0.929 |
|29.4 | 0.954 | 0.949 | 0.943 | 0.938 | 0.932 |
|29.5 | 0.957 | 0.952 | 0.947 | 0.941 | 0.936 |
|29.6 | 0.960 | 0.955 | 0.950 | 0.944 | 0.939 |
|29.7 | 0.964 | 0.959 | 0.953 | 0.948 | 0.942 |
|29.8 | 0.967 | 0.962 | 0.957 | 0.951 | 0.946 |
|29.9 | 0.970 | 0.965 | 0.960 | 0.954 | 0.949 |
|30.0 | 0.974 | 0.968 | 0.963 | 0.958 | 0.952 |
|30.1 | 0.977 | 0.972 | 0.966 | 0.961 | 0.955 |
|30.2 | 0.980 | 0.975 | 0.970 | 0.964 | 0.959 |
|30.3 | 0.984 | 0.978 | 0.973 | 0.968 | 0.962 |
|30.4 | 0.987 | 0.982 | 0.976 | 0.971 | 0.965 |
|30.5 | 0.990 | 0.985 | 0.980 | 0.974 | 0.969 |
|_____|_______|_______|_______|_______|_______|
For the detection of phosphine, Bergé's solution may be used. It is a "solution of 8 to 10 parts of corrosive sublimate in 80 parts of water and 20 parts of 30 per cent. hydrochloric acid." It becomes cloudy when gas containing phosphine is passed into it. It is, however, applied most conveniently in the form of Keppeler's test-papers, which have been described in Chapter V. Test-papers for phosphine, the active body in which has not yet been divulged, have recently been produced for sale by F. B. Gatehouse.
The estimation of phosphine will usually require to be carried out either (1) on gas directly evolved from carbide in order to ascertain if the carbide in question yields an excessive proportion of phosphine, or (2) upon acetylene which is presumably purified, drawn either from the outlet of the purifier or from the service-pipes, with the object of ascertaining whether an adequate purification in regard to phosphine has been accomplished. In either case, the method of estimation is the same, but in the first, acetylene should be specially generated from a small representative sample of the carbide and led directly into the apparatus for the absorption of the phosphine. If the acetylene passes into the ordinary gasholder, the amount of phosphine in gas drawn off from the holder will vary from time to time according to the temperature and the degree of saturation of the water in the holder-tank with phosphine, as well as according to the amount of phosphine in the gas generated at the time.
A method frequently employed for the determination of phosphine in acetylene is one devised by Lunge and Cedercreutz. If the acetylene is to be evolved from a sample of carbide in order to ascertain how much phosphine the latter yields to the gas, about 50 to 70 grammes of the carbide, of the size of peas, are brought into a half-litre flask, and a tap-funnel, with the mouth of its stem contracted, is passed through a rubber plug fitting the mouth of the flask. A glass tube passing through the plug serves to convey the gas evolved to an absorption apparatus, which is charged with about 75 c.c. of a 2 to 3 per cent. solution of sodium hypochlorite. The absorption apparatus may be a ten-bulbed absorption tube or any convenient form of absorption bulbs which subject the gas to intimate contact with the solution. If acetylene from a service-pipe is to be tested, it is led direct from the nozzle of a gas- tap to the absorption tube, the outlet of which is connected with an aspirator or the inlet of an experimental meter, by which the volume of gas passed through the solution is measured. But if the generating flask is employed, water is allowed to drop from the tap-funnel on to the carbide in the flask at the rate of 6 to 7 drops a minute (the tap-funnel being filled up from time to time), and all the carbide will thus be decomposed in 3 to 4 hours. The flask is then filled to the neck with water, and disconnected from the absorption apparatus, through which a little air is then drawn. The absorbing liquid is then poured, and washed out, into a beaker; hydrochloric acid is added to it, and it is boiled in order to expel the liberated chlorine. It is then usual to precipitate the sulphuric acid by adding solution of barium chloride to the boiling liquid, allowing it to cool and settle, and then filtering. The weight of barium sulphate obtained by ignition of the filter and its contents, multiplied by 0.137, gives the amount of sulphur present in the acetylene in the form of sulphuretted hydrogen. The filtrate and washings from this precipitate are rendered slightly ammoniacal, and a small excess of "magnesia mixture" is added; the whole is stirred, left to stand for 12 hours, filtered, the precipitate washed with water rendered slightly ammoniacal, dried, ignited, and weighed. The weight so found multiplied by 0.278 gives the weight of phosphorus in the form of phosphine in the volume of gas passed through the absorbent liquid.
Objection may rightly be raised to the Lunge and Cedercreutz method of estimating the phosphine in crude acetylene on the ground that explosions are apt to occur when the gas is being passed into the hypochlorite solution. Also it must be borne in mind that it aims at estimating only the phosphorus which is contained in the gas in the form of phosphine, and that there may also be present in the gas organic compounds of phosphorus which are not decomposed by the hypochlorite. But when the acetylene is evolved from the carbide in proper conditions for the avoidance of appreciable heating it appears fairly well established that phosphorus compounds other than phosphine exist in the gas only in practically negligible amount, unless the carbide decomposed is of an abnormal character. Various methods of burning the acetylene and estimating the phosphorus in the products of combustion have, however been proposed for the purpose of determining the total amount of phosphorus in acetylene. Some of them are applicable to the simultaneous determination of the total sulphur in the acetylene, and in this respect become akin to the Gas Referees' method for the determination of the sulphur compounds in coal-gas.
Eitner and Keppeler have proposed to burn the acetylene on which the estimation is to be made in a current of neat oxygen. But this procedure is rather inconvenient, and by no means essential. Lidholm liberated acetylene slowly from 10 grammes of carbide by immersing the carbide in absolute alcohol and gradually adding water, while the gas mixed with a stream of hydrogen leading to a burner within a flask. The flow of hydrogen was reduced or cut off entirely while the acetylene was coming off freely, but hydrogen was kept burning for ten minutes after the flame had ceased to be luminous in order to ensure the burning of the last traces of acetylene. The products of combustion were aspirated through a condenser and a washing bottle, which at the close were rinsed out with warm solution of ammonia. The whole of the liquid so obtained was concentrated by evaporation, filtered in order to remove particles of soot or other extraneous matter, and acidified with nitric acid. The phosphoric acid was then precipitated by addition of ammonium molybdate.
J. W. Gatehouse burns the acetylene in an ordinary acetylene burner of from 10 to 30 litres per hour capacity, and passes the products of combustion through a spiral condensing tube through which water is dropped at the rate of about 75 c.c. per hour, and collected in a beaker. The burner is placed in a glass bell-shaped combustion chamber connected at the top through a right-angled tube with the condenser, and closed below by a metal base through which the burner is passed. The amount of gas burnt for one determination is from 50 to 100 litres. When the gas is extinguished, the volume consumed is noted, and after cooling, the combustion chamber and condenser are washed out with the liquid collected in the beaker and finally with distilled water, and the whole, amounting to about 400 c.c., is neutralised with solution of caustic alkali (if decinormal alkali is used, the total acidity of the liquid thus ascertained may be taken as a convenient expression of the aggregate amount of the sulphuric, phosphoric and silicic acids resulting from the combustion of the total corresponding impurities in the gas), acidified with hydrochloric acid, and evaporated to dryness with the addition towards the end of a few drops of nitric acid. The residue is taken up in dilute hydrochloric acid; and silica filtered off and estimated if desired. To the filtrate, ammonia and magnesia mixture are added, and the magnesium pyrophosphate separated and weighed with the usual precautions. Sulphuric acid may, if desired, be estimated in the filtrate, but in that case care must be taken that the magnesia mixture used was free from it.