328 THE COLLIERY GUARDIAN. February 14, 1913. Table 2.—Results Showing Percentage Lost by Coal when Tested by Methods for Determination of Water Ordinarily Employed by Members of Sub-Committee^ Particulars of method. Coal Number. vv oi’Ker. Grammes of coal. Weighed in Heated in Hours. 1. 2. 3. 4. 5. 6. I. 1 — Gay Lussac water oven at 98—99 degs. 2 2*90 9*70 7*10 5’30 7*10 7*20 II. 25—30 Brass tray closed when weighing. Water oven (air oven) at 100 degs., 105—110 degs. Constant) weight. ) 3*15 10*03 7*44 5*91 7*36 7*84 III. — Covered copper crucible. Drying stove with air circulation at 105 degs. { 2 88 o.qi? 2*87) 2 87 9'27} 9 20 t-If}6'68 5’36 7 ~.QQ 5*39 V 88 t^W2 72517*24 7 23 5 ' IV. 1 Porcelain crucible. Toluene bath at 104—107 degs. 1 3*11 10*06 7*74 6*08 7*56 7*66 V. 1 Platinum crucible. Steam oven under pressure at 105 degs. 1 2*75 9*63 7*37 5*77 7*09 7’31 VI. 4—5 Watch glasses clipped. Toluene oven. 1 3*15 9*57 7*43 5*32 7*33 7*58 VIE. 1 Shallow weighing bottle. Toluene oven at 108 degs. 1 £ 2'9812'97 & yo y 10*16 7 10’16 ) 10 16 7 54 7 h. t-n 7’64) 1 5y ^H5'98 7*98 } 7*95 VIII. 1 Weighing bottle. At 105 degs. 1 { 3*06 5 o-i t- 3*24 ) 8 ib 9*82 7 9*92) y 87 7-4fi I 7-40 7 46 ) 614 IX. 4 Porcelain boat weighed in tube. Water oven with hot air circulation at 1 2*90 9*69 7 36 5*40 7*06 7 38 X. 94—95 degs. 1 Porcelain crucible. Air bath at 105 degs. 3*16 10*16 7*79 6*19 7*34 7*45 XI. 1 Watch glasses clipped. V. Meyer toluene oven. 1 2*95 9*86 7*34 5*95 7*28 7*45 XII. 1 Watch glasses ground to fit. Water oven. 1 3*12 9*78 7*28 5*46 7*31 7*66 XIII.* — — ' — i — — — XIV. i f 3*04') 9*98) 7*511 6*201 7’561 7*711 1 Weighing bottle laid on side. Drying stove at 100—110 degs. mean 3*10 >3’05 10*03 >10’03 7*53 [■ 7*52 6*13 >6’19 7*47 >7*51 7*87 5- 7*78 105 degs. 3’00 ) 10*09) 7*52 ) 6*24) 7*51) 7*77) XV. 1 j Weighing bottle. Large toluene oven at 103 degs. i 2 { 2’9812 99 0’59 7 9*62 ) y 01 7>-18 f^b-52 D DO ) 7 09 7 iq 7*17) 7 13 7’44 7 40 7*425/4B XVI. 2 Watch glasses tared against Water oven. iTo constant 2*90 9*48 7 12 5*24 695 7*07 l similar glasses. 1 weight. Maximum 3*16 10*16 7*79 6*19 7*64 7*95 Minimum 2*75 9*30 6*68 5*27 6 92 7*07 Average of average results 2*99 9*76 j 7*33 5*71 7*23 7*47 * See remarks on the table. Table 3.—Results Obtained by Drying in a Vacuum. Particulars of method. Coal Number. Worker. Weight taken. Weighed in Time. Desiccator. 1. 2. 3. 4. 5. i 6. I. 1 gramme. 36 hours. H2SO4. 2*79 9*60 7*10 5*20 7*00 7*10 II. — Porcelain dishes. Constant weight after h2so4. 1 Vacuum 12 mm. Hg. > 2*41 9*01 5*93 3*99 5*98 6*87 3 days. 4’58 Y III. 1 Porcelain dishes. Constant weight H2SO4 (1*84 sp. gr.). | 2’56 7 o-i 2*65 ) 2 bl 9’89 7 q.oq 9*87 5 y 88 7’00 7 0.Q? 6*94) byz 4'72 f 4*52 C 4 bi 6*77 7 6*86) 6 8j 7’10 7 7*03 5 ‘ 07 36 hours. 4*60 J IV. 1 ,, — — h2so4. 3*11 10'32 7*76 5*81 7*60 7*80 V. 2 — 24 hours. 2*85 10’17 7*54 5*52 7 51 7*68 VII. — Shallow weighing bottle. 15 hours. Fresh H2SO4 (1*84 sp. gr.). j loll}10'12 ?:8>87 3:99}6-o8 ?^7'33 7$}7’96 24 hours. V acuum 1—3 mm. 7 3 70 } 3 33 win1037 rio}7'83 00} 605 7-72}7'68 Tu}836 VIII. 1 >> Weighing bottle. 24 hours. Strong H2SO4. £ 2*84 2*84 8*80 9*04 6*42 6*62 3*84 3*90 6*41 6*46 7*16 7*04 IX* — . — — 2*92 9*96 7’52 5 42 7*26 7*56 X. — — 24 hours. Strongest H2SO4. ( 3*11 10*25 7*88 6*05 7*74 8*02 48 hours. Desiccator gently moved occa- < 3*12 10*33 7*98 6’22 7’79 8*08 sionally. 7’66 7*82 XI. — Clipped watch glasses. 24 hours. Hempel. Strong H2 SO4. ) 3*09 10*31 10*38 10*37 7*74 6*13 Vacuum 20 mm. Hg. 1 XII. 1 Boat or weighing tube. Till Strong H2SO4 except ini 7*52 7*76 XIII. constant. 1 (P2O5 used) Vacuum > 12 mm. Hg. ) 2*85 10*03 7*52 5*44 1 ,, Porcelain crucible. 24 hours. H2SO4 66 B. (50 mm. Hg.). 2*60 9*60 7’20 4*90 6*80 7’10 XIV. 1 33 Weighing bottle. Every 24 hours till h2so4. 1 2’95 7 0.94 2*92 5 10’027 in.ni 10*00510 v 7*52 7 7.50 7*54 5 7 58 5’75 ? K.^o 5*68 ) 5 72 XV. constant. 1 Weighing bottles, 28 mm. To constant P2O5. £ 2*98 10*26 7*81 6*11 7*66 7*75 XVI. diam., 22 mm. high. weight. 2*95 10*27 7*79 6*08 7*68 7*71 1 — To constant H2SO4 below samples pre- 2*85 9*63 7*20 5*07 7*00 7’11 weight. ferred. Maximum 3*70 10*39 7*98 6*22 7 79 8*41 Minimum 2*41 9*01 5*93 3'84 . 5*98 6 87 Average 2*95 9*97 7*40 5*35 1 7*27 7'60 * No details. it, are exposed to a confined atmosphere are in equilibrium. A reduction, by evacuation, of the partial pressure of other gases or vapours than water will accelerate this process which, except when the initial difference of vapour tension is very high—e.g., at high temperatures—will always be very slow. The rate of drying will—if, as is most probably the case, the water is absorbed (retained by surface concentration)—follow an exponential curve, the slope of which will depend on the rapidity of the exchange through the medium of the vacuous space between the substance to be dried and the desiccant. If the temperature be kept constant this rate will vary with the relative areas of substance and desiccant which are exposed, with the partial pressure of gases other than water vapour, with the absorptive power—i.e., the vapour pressure of the desiccant, with the volume and form of the vacuous vessel used and the form of the vessel in which the substance to be dried is exposed. In any case the drying, relatively rapid at first, will soon fall off to a nearly uniform rate which may continue for days, and the increments of the loss of weight may be so small as to appear negligible, whereas their sum over the whole period of drying would perhaps be appreciable. In fact, it is difficult to know when to stop. The results actually obtained by workers bear out this conclusion. In a method such as this, which is practically free from manipulative errors, it is difficult to explain the great variations obtained by different workers otherwise than by supposing that stagnation of vapour, differences of temperature, small exposure of substance to be dried or of desiccant account for the lowness of some of the results. It may be supposed that in all these cases much longer exposure would have caused a greater loss, although there is the chance that even with a fairly good vacuum some compensating gain by oxidation may take place, thus invalidating any results obtained in a badly designed desiccator or with a weak desiccant. When the lowness of the vacuum is a cause of slow drying, this possibility of oxidation becomes still greater. We may consider the series VII. conducted in a relatively very high vacuum. The results obtained by drying in 24 hours are in four, or say three, cases out of six much higher than those obtained in 15 hours. One naturally asks what would the results of 48 or 96 hours drying be ? Possibly the same as those given ; but who knows ? Where is finality ? Profs. De Koninck and Huybrechts weighed the samples examined by them at intervals, and tabulated * the results; for example, we give those obtained with | Nos. 2 and 4:— After drying in vacuo over H2SO4 for Hours. ^24 48 62 96 12(P the loss was— Ar o < 8*66 ... 9 55 ... 9*76 ... 9*97 ... 10*02 JNo*2.... <8’66 ... 9*56 ... 9*74 ... 9*94 ... 10*00 ( 5*47 ... 5*57 ... 5*75 ... 5*57 ... 5*44 JNo* 4 .. I 5*38 ... 5*52 ... 5*68 ... 5*57 ... 5*49 Here we see that whilst No. 2 dried continuously at a slowly decreasing rate during five days, No. 4, which was of an exceptional character, reached a maximum loss in three days and then began to gain. One may ask again of No. 2, what virtue is there in the maximum period adopted? Judging from the form of the curve and the magnitude of the last loss observed, it might be expected that the coal should go on losing a few hundredths of a per cent, for some days * Or what data for the true determination of water do the figures for No. 4 afford ? How much lower is the figure 5*68 than the true water content ? When did the oxidation, which has undoubtedly occurred, begin to be appreciable ? What would be the result of displacing the air in the desiccator with an inert gas before evacuating ? Another question which is perhaps not altogether academical arises: Is all the loss moisture, or do hydrocarbon and other gases escape from coal under the conditions of experiment ? Experiments by Dr. Pollard with the sample No. 2 showed that when this coal was dried in vacuo at 105 degs. and the loss of weight of the coal determined as well as the gain in weight of sulphuric acid drying tubes, only a very small difference was found, the results being: direct, 10*67 per cent.; loss, 10*58 per cent. This difference, it should be noticed, was in the direction usually observed, the direct result being the higher pointing to oxidation rather than to excessive loss in a vacuum. Experiments by him with ferrous sulphate showed that this salt was invariably oxidised when dried in an “ air vacuum,” but not so in a “ hydrogen vacuum.” * Of. Hillebrand, Bulletin 422, U.S. Geological Survey, p. 68.