DR. ANDREW ON THE LATEST HEAT OF VAPOURS. ANDREWS, IV. On the Latent Heat of Vapcurs. By THOMAS M.D. M.R.I.A. SINCE the period when Black first explained his celebrated doctrine of Latent Heat and showed the general method of measuring the quantities of heat evolved or abstracted during the changes of bodies from one physical state to another the subject has attracted the attention of several distinguished inquirers both in this country and on the continent It would be foreign to my present purpose to enter into a detailed account of their methods or results which is indeed the less necessary as a very complete history of the subject accompanied by critical remarks will be found in an able Memoir published a few years ago in Poggendorff’s Annalen,* by Dr.Brix of Berlin More recently two important communications on this subject have been made to the Academy of Sciences of Paris; one by M. Regnault on the Latent Heat of Steam when generated under different pressures; the other by MM. Favre and Silbermann on the Latent Heat of the Vapours of several Organic Liquids. My object in entering upon this inquiry was not to attempt a new determination of the latent heat of aqueous vapour but to extend the investigation to the vapours of other bodies differing widely from one another in chemical composition with the view principally of ascer- taining whether any fixed relation exists between the latent heat and * Bd. LV. s. 341. DE. ANIIREWS ON THE LriTENT HEAT OF VAPOURS. the other physical properties of vapours.In this inquiry I have been preceded by Ere Despretz Brix and Fabre and Silbermann. Their results are for the most part remarkable for accuracy but with the exception of those of the last-named experimentalists extend only to a very small number of substances. Even their experiments how- ever only embrace compounds of oxygen hydrogen and carbon. By employing a very delicate glass xpparatus 1have been enabled to supply in some measure this deficiency and to extend the inquiry to one simple substance and a small number of inorganic com-pounds . The apparatus employed in these experiments is represented in Fig. 1. The fluid to be converted into vapour is placed in a FIG. 1. small glass flask the iieck of which has a very short bend as shown in the figure.Into this the end of the rccciver is inserted by means DR. ANDREWS ON THE LATENT HEAT OF VAPOURS. of a small cork. The form of the receiver is shown in Fig 2. It consists of a very thin bulb of German glass terminating in a spiral tube of the same material. The glass receiver is fixed by a cork in a light copper vessel (Fig. 3) from which it 'can be FIG. 3. easily removed at the end of the experiment. The copper vessel which is open above is filled with water cooled from loto 2O C. (lo%-3'*6F.) below the temperature of the air. The whole is surrounded by an outer vessel of tin-plate fitted with a moveable lid in which are three openings one for the thermometer another for the extremity of the spiral tube of the receiver and a third for the stirrer which is formed of a very light and hollow glass tube.An additional screen as shown in the figure is interposed between the lamp by which the liquid is heated and the rest of the apparatus. The thermometer employed is very delicate and the greatest pains were taken to insure its accuracy. The diameter of the reservoir is not greater than that of a thin thermometer tube and it occupies the entire depth of the calorimeter. It is attached to an arbitrary metallic scale divided into fiftieth parts of an inch. The errors of calibre were determined by two distinct measurements of columns of mercury of different lengths ; the freezing point was ascertained by direct observation and another point situated near 25O C.(770F.) by comparison with an accurate thermometer constructed by Greiner. It was easy from these data to prepare a table showing the degree corresponding to each arbitrary division of the scale and also the multiplier required to reduce an increment observed at any part of the scale into true degrees. Two independent tables were constructed from the separate measurements and they were found to differ nowhere more than OO.01 C. (0".018F.). Within the ordinary limits of atmospheric temperature the difference of the expansion of a metallic or glass scale for increments of a few degrees is so slight that it may be neglected. The correction for the mercury in the stem of the thermometer is more important. The multipliers for the divisions of the arbitrary scale were corrected accordinply.DR. ANUREWS ON THE LATENT HEBT OF VAPOUILS. The increments of temperature as obtained by observation were carefully corrected for the cooling and heating influence of the surrounding air. From one to two minutes were occupied in raising the liquid to the point of ebullition; and during this period the thermometer remained nearly at the same point. While the ebullition continued the t,hermometer rose very steadily and uniformly but it did not attain the maximum point till about two minutes after the ebullition had ceased. For the heat gained and lost during these periods a correction deduced from direct experiments with the calorimeter alone was applied. The agitation was continued for five minutes after the thermometer had reached the maximum and the difference between the loss of heat observed and that indicated by calculation was added as a further correction to the result.This last is frequently omitted in inquiries such as the present but it generally amounts to an appreciable quantity and in accurate experi- ment ought never to be neglected. To prevent the mercurial column from becoming heated by the person of the observer the divisions were read through a powerful magnifier which was fixed on a moveable support. In addition to the causes of error already referred to others exist of' not less importance but the effect of which it is much more difficult to estimate. If the liquid be boiled too slowly a portion of the vapour will be condensed in the tube of the receiver just before it enters the calorimeter and a considerable loss of heat will occur.On the other hand if the ebullition is carried on very rapidly an undue pressure will be produced in the interior of the retort the tempera- ture of the vapour will be raised above the ordinary boiling point and too large an increment finally obtained. A portion of uncon-densed but partially cooled vapour will also escape particularly at the commencement of the operation before the air has been expelled. On this part of the subject an elaborate mathematical investigation will be found in the memoir of Dr. Brix to which reference has already been made; but it may be doubted whether the experimental data are yet sufficiently precise to admit of the useful application of formulas derived from the higher branches of analysis.To ascertain as far as possible the limits of error to which the apparatus now described is liable I made two series of experiments with water and alcohol; in the first the ebullition occupied from one and a half to two minutes; in the second from three and a half to five minutes. In order to complete the operation in the shortest period the liquid was made to boil very violently and there can be no doubt that the vapoiir was generated under a higher pressurc than that of the DR. ANDREIT'S ON THE LATENT HEAT OF VAPOURS. atmosphere. In the other case the ebullition proceeded at a gentle rate and all the causes of error tended to render the results too low.The mean number given by the experiments of the first series for the latent heat of water was 541O.4 C. (1038@*5 ) ;and by those of the F second 532O.7 C. (1023"F.). The mean of the whole was 535O-9 C. (1030"*75F.). This latter number agrees very closely with the mean of the results obtained by Despretz Dulong and Brix and is almost identical with that recently arrived at by 34. Regnault.* From these observations it follows that when the operation was purposely so performed as to exaggerate to the utmost the errors occasioned by the apparatus the result does not diverge more than Ath part from the true number The experiments with alcohol lead to the same conclu- sion; the mean of the series in which the ebullition occupied the shortest period being 205O.O C.(401' F.) and of that in which it occupied the longest period 202O.4C. (396"3 F.); so that the diffe- rence here was even less than in the experiments with water. In deter- mining the latent heat of other bodies the fluid was made to boil as fast as was possible without producing increased pressure on the interior of the apparatus. In the case of a few liquids it was found difficult to complete the vaporization in the ordinary time and hence the results expressing their latent heats are probably a little below the true numbers. This remark applies particularly to the iodic and oxalic ethers and to the iodide and acetate of methyl. The weight of the condensed vapour was ascertained by weighing the glass receiver (Fig.2) at the end of the experiment and deducting the weight of the same when empty. The boiling points of all the liquids operated on were determined with great care. This is often attended with considerable difficulty and even distinguished chemists have committed serious mistakes in examining the boiling points of volatile fluids. The numbers given in this paper were obtained by heating the liquid with a very small spirit flame in a glass retort the thermometer being immersed in the vapour at a short distance above the surface of the liquid. A quantity of mercury was placed in the retort except in the case of liquids which attacked that metal. The results given by observation were corrected for the portion of mercury in the stem of the thermo- meter which was not heated in the rapour and also for the variations of the barometer.In making the latter correction it was assumed as a sufficient approximation that the boiling points of other liquids were raised or depressed to the same extent as that of water by the same changes in the height of the barometer. * Their numbers are 531 Despretz ; 543 Diilong; 540. Brix ; 536.4 Regnaiilt. 32 DR. ANDREWS ON THE LATENT HEAT OF VAPOURS. The specific heats of several of the liquids were deteriiiiiied by direct experiment. The liquid raised to the boiling point was quickly int,roduced into a thin glass tube immersed in water and the gain of heat of the latter observed. The results in general agreed very closely with those of Regnault.In other cases I have employed the numbers given by the same accurate observer which were in general deter- mined by observing their rates of cooling. A slight error may thus be produced in consequence of the specific heat of the liquid not being the same at different temperatures but for the liquids actually employed this difference is probably unimportant. Finally every precaution was taken to operate on perfectly pure chemical substances. This is of much more importance in such inquiries as the present than even in analytical investigations from the great differences in the specific heats of the same weight of different liquids. Thus the presence of only ,&th part by weight of aqueous vapour would induce an error of +th part in the determi- nation of the latent heat of the vapour of ether.The weight and thermal value in ternis of water of the different parts of the apparatus were as follows Copper vessel 49.5 grms. x 0.095 4-7grms. Glass receiver 13.7 x 0.183 25 Thermometer stirrer and cork . . . 0-5 -Thermal equivalent of apparatus . . . 7.7 grnis. In stating the results I have used the following abbreviations Bar. the height of the barometer reduced to 0. Air the temperature of the air in centigrade degrees. Ex. the excess of the final temperature of the water in the calori- meter above the air. Inc. the increment of temperature as obtained by observation. T the time of ebullition. Ti the time from the observation of the initial temperature till the thermometer attained its maximum.V the weight of condensed vapour. W the weight of the water in the calorimeter exclusive of the thermal value of the vessels. L.H. the latent heat corrected. PVuter.-Specific heat 1*OO. Boiling point under a pressure of 29.92 inches at 100" C. (212' F.). FIRST SERIES. I. 11. 111. Bar. 29.52 in. 30.43 30.14 DR. ANDREWS ON THE LATENT HEAT OF VAYOVRS* I. 11. 111. I\-. Air. 6O.50 8O.60 9”*90 Ex. 2O.69 aO*oo 10.97 Inc. 4O-083 3”*411 3O.761 T 1’,20” 1’,35” 1I 50” T 3’,45” 3’,30” 5’,0 V 1.860 gm. 1.573 gm. 1.766 gin. W 2792.2grms. 282.3grms. 286.2 grim. L.H. 542.9 543.4 537.9 Mean latent heat 541.4. SECOND SERIES. I. 11. 111. IV. V. Bar. 29.70 in. 30.10 in. 30.10 in. 30.15 in. 30.09 in.Air. 11O.30 100.10 1OO-44 90.55 10°*20 Ex. 2O.08 lo-87 2O.20 10.83 10.78 Inc. 3O.772 3O.833 4O-078 4O.039 3O.822 T. 4,35” 4’,0” 3’,15” 3’,35” 5’,0 T. 7’,10” 6’,15” 5’,45” 5’,40” 6’,55‘ V. 1.780 gm. 1.829 gm. 1.980 gm. 1.921 gm. 1.833gin. W. 285.1 grms. 287.8 grms. 293.8 grms. 287.7 286.7grms. L.H. 536.8 531.9 533.2 531.6 530.8 Mean latent heat 532.7. Mean of whole series 535.9. Alcohol.-The alcohol was purified by repeated distillations from lime in a vapour-bath. It was deprived of essential oil by charcoal. It boiled at 78O.3 C. (173O.O F.) under a prsssure of 30.3 in.; and hence its true boiling point under a pressure of 29.9 in. is 77’9 C. (172O.3 F.). The mean of three experiments gave for its specific heat 0.617. FIRST SERIES.I. 11. 111. Bar. 29.75 in. 29.75 in. 29.73 Air. 14O-20 14O.95 14O.55 Ex. 1O.50 20.00 2-29 Inc. 3O.467 30.367 3.633 T. 1’,55” 2’,0” 1’,45” T. 4’,25” 4’,40” 4’,40’’ V. 4.202 gms. 4.167 gms. 4.418 gms. w. 286-0 , 289-4 , 286.8 L.H. 204.8 203.9 206.2 Mean latent beat 205.0. VOL. I. NO. I. D DR. ANDREWS OX THE LATENT HEEAT OF VAPOURY. SECOND SERIES. I. 11. 111. I\’. v. Bar. 29.90 in. 29-90 in. 29.91 29.91 29.90 Air. 1lo.1O 1l0*1O 10°*80 10O.70 10°.60 Ex. 2O.38 10.90 1O.56 1O.92 1O.72 Inc. 4O.417 3O.833 3O.533 3O.878 3O.567 T. 4‘,25” 4’,35” 3’,40” 3’,50” 4’,25” T’. 6’,401’ 6’,45” 4‘ 55” 5’,25’’ 6’,0” V. 5.381 gms. 4.785 gms. 4.402 gms. 4.830 gms. 4.430 gms. TIr. 286.3 , 292.2 , 293.0 , 291.4 , 289.5 L.H.201.7 201.4 201.5 199.7 199.7 Mean latent heat 200.8. Mean of whole series 202.4. Brornine.-Pure bromine according to my experiments boils under a pressure of 29.9 in. at 58O C. (136O.6 F.) and its specific heat is 0*107.* I. 11. 111. IV. Bar. 30-01in. 29.99 in. 29.70 in. 29-70 in. Air. 6O.30 6O-50 5O70 5O-70 Ex. 1O.33 lo-28 1O.33 1O.55 Inc. 2O.659 2O.708 2O.568 2O.975 T. 2‘,45” 3’,30” 3’,55// 2’,55” T. 5’,30” 6’,30” 6’,45” So 15” V. 14.983 gms 15.291 gms. 14.638 gms. 16.910 gms. W. 279.8 , 279-2 , 279.3 , 279.2 , L.H. 45-95 45.62 45.28 45.56 Mean latent heat 45.60. Protochloride of Phosphorus.-The protochloride was prepared by the action of dry chlorine gas on phosphorus. It was afterwards digested for several days with an excess of phosphorus and purified by repeated distillations.It was perfectly limpid and colourless. and under a pressure of 30.20 in. it boiled at 78O-5 C. (173~4~ F.) I have taken Regnault’s number (0.209) for its specific heat. I. 11. 111. Bar. 29.54 in. 29.29 in. 29.49 in. Air. 4O.90 7O.16 1OO.33 Ex. 1O.67 20.I 1 2O.21 7 Inc. 2O556 3n*0.1 3.733 T. 2’,30” 2’,35” 3’,5” * See present number p. 19. Dlt. ANDREWS ON THE LATENT HEAT OF VAPOURS. I. 11 111. T’ 5’,30” 5’,30” c,’ 0” V. 11.245 gms. 13.122 gms. 16.531 gins. W. 280.0 , 276.5 , 278.0 , L.H. 51.11 51.77 51-39 Mean latent heat 51.42. Bichloride of Tin.-This compound was prcpared by the action of dry chlorine on tin and after being deprived of the excess of chlorine by digestion with tin filings was purified by repeated distillations.It boiled at ll2O.5 C. (233O.9 F.) under a pressure of 29.60 in. Its specific heat was assumed to be 0.148. I. 11. 111. Bar. 30.12 in. 30.12 in. 30.17 in. Air. 6O.10 6O.10 6“40 Ex. 1O.64 1O.55 1O.28 Inc. 2O-578 3O.006 2O.700 T. 2‘ 15’’ 2’,0” 2’,45” T 6,30” 5’,30’’ 6’,0” V. 16.232 gms. 18.555 gins. 16.924 gms. W. 278.8 , 278.8 , 278.8 L.H. 30-37 31-02 30.21 Mean latent heat 30.53. Su(~7zuretof Carbon.-This liquid was digested with chloride of calcium and distilled It boiled under a pressure of 30.30 in. at 46O.2 (115O F.) Specific heat assumed to be 0.319 (Regnault). I. rr. 111. Bar. 29.92 in. 30.27 in. 30.27 in. Air. 9O.10 9O.05 8O.94 Ex.2O.83 3O.00 P44 Inc. 4O.422 4O.467 4O.761 T. 3’,30” 3‘,0“ 3’,45 ’ T‘. 535“ 5’,30“ 6’,25” V. 13.465 gms. 13.618 gms. 14.548 gms. W. 276.7 , 276% , 277.1 , L.H. 86.72 86-56 86-72 Mean latent heat 86.67 Subhuric Ether.-This ether was purified in the usual manner. It boiled under a pressure of 29-61 in. at 34O.9 C. (94O.73 F.) Specific heat 0.517. D2 DR ANDREWS ON THE LATENT HEAT OF VAPOURY. I. 11. 111. Bar. 30.18 in. 30.16 in. 30.16 in. Air. 2O.30 8@*10 8O.10 Ex. lo-78 lo*% 2O.11 Inc 3O.783 3O.5 72 3O.806 T. 4/>15” 3‘,50” 3/,50” T’. 6’,25” 6’ 10” 6’,20” V. 10.477 gms. 9.812 gins. 10.473gms. W. 277.0 , 277.1 , 2765 , L.H. 89.89 90.94 90.50 Mean latent heat 90.45. Iodic Ether.-This ether was prepared by taking 14 gms.phos-phorus and 70 gms. alcohol sp. gr. 0.816 and adding in small portions 46 gms. iodine waiting between each addition of iodine till the liquid became clear. It was then distilled at a gentle heat washed with water and allowed to digest for forty-eight hours with an excess of chloride of calcium. It was again didlled at a tempera-ture of from 70° to 75O. (1d8°-1670 F.) The purification was finally completed by another digestion with chloride of calcium and distillation. Its boiling point was found to be 71O.3 (160O.36 F.) under a pressure of 29.9 in. I. 11. 111. IV. Bar. 29-53in. 29.39 in. 29.40 in. 29-40 in. Air. 7O-70 7O.05 7O.90 8@*05 Ex. 2O.39 1O.72 2O.28 2O.44 Inc. 3O.939 3O.294 3O.717 4O.256 T. 5’,35” 6’,5” 6/,0” 6’,0” T!.8’,20” 9’,20” 8’ 55” 9/,30” V. 20974 gms. 17-504gms. 19.590 gms. 22.170 gms. W. 289.6 , 292.1 , 285.2 , 283-7 L.H. 46.94 46.78 46.83 46.94 Mean latent heat 46-87. OxaZic Ether.-The oxalic employed in the following experiments boiled at 184.4 (396O F.) under a pressure of 30.7 in. Specific heat 0-45 7. 1. 11. m. Bar. 30.66 in. 30.60 in. 30.60 in. Air. 6O.20 7O.50 7O.60 Ex. 2O.89 1O.50 2O.89 Inc. 4O.744 3O.772 4O.333 T. 3’,10” 5/,35” 3’,15‘‘ DR. ANDREWS ON THE LATENT HEAT OF T‘APOURS. 37 1 11. 111. T’. 7’,25” 9’ 5 0” 8’,30” V. 9.177 gms. 7.335 gms. 8.4161 gms. W. L.H. 284.3 73-33 , 288.5 72.61 , 284.8 72.22 , Mean latent heat 72-72. Acetic Ether.-This ether carefully purified was found to boil at 74O.6 (166O.36 F.) under a pressure of 30 in.Its specific heat in two trials was found to be 0-471 and 0.477 ; mean 0.474. I. 11. 111. IV. Bar. 29.92 in. 29.90 in. 29.90 in. 29-89 in. Air. 1O”20 10”*50 1OO.90 11O.10 EX. 2O.33 1O.94 1O-56 1”-78 Inc. 4°*500 4O.012 3O.967 3O.711 T. 5’,5”’ 3’,50” 3’,10” 3’,35” T. 8’,35” 6,45” 5‘,45“ 6’,30’’ V. 10.804 gms. 9-524 gms. 9,468 gms. 8.761 gms. w. 283.0 , 283.7 , 281.3 , 279.6 , L.H. 92-22 93.72 92.00 92.78 Mean latent heat 92.68. Formic Ether.-The easiest method of procuring formic acid for the preparation of this ether is by distilling rapidly hydrated oxalic acid. On neutralizing the acid liquid which passes over with carbo- nate of soda the greater part of the oxalic acid precipitates in the form of oxalate of soda and by evaporation the formiate of soda mixed with a little oxalate is obtained.This may be etherified without further purification as the formic ether is easily and com- pletely separated from the oxalic by distillation. Formic ether thus obtained probably furnishes the easiest means of procuring formic acid and its salts in a state of purity. Formic ether boils under a pressure of 30 in. at 54O.3 (2290.9 F.). In three experiments its specific heat was found to be 0.485 0.437 and 0.490; mean 0.485. I. 11. 111. IV. Bar. 29-83 in. 29.57 in. 29.57 in. 29.57 in. Air. 11”.05 9’-20 9O.67 9”-55 Ex. 1”*94 2”OO 1O.78 2O.28 Inc. 4°*006 3O.572 3O.439 4O.061 T. 2’,45” 3’,50” 3’,55” 1’,40” T’. 5’,30” 6’,20” 6’,25” 4’ 10” V.9.323 pis. 8.508 gnis. 8-092pis. 9.379 gins. DH. ANDREWS ON THE LATENT HEAT OF VA4POUBS. 1. 11. 111. IV. W. 281.9 gms. 2884 giiis. 283.6 gins. 282.6 gnis. L.H. 105.3 105.0 104.2 106.7 Mean latent heat 105.3 Methylic Acohol.-The pyroxylic spirit of commerce was rectified several times over a water-bath from an excess of lime the first and last portions being rejected. It was afterwards combined with chloride of calcium and purified according to the method of Kane. It boiled at 65O.8 (150O.72 F.) under a pressure of 30.2 in. In two experiments the numbers obtained for its specific heat were 0.611 and 0.615 ;mean 0.613. 1. 11. 111. Bar. 29-72 ill. 29.72 in. 29.71 in. Air. 1l0.1O 11”*90 l2“20 Ex. 2”50 1’0.61 2’%1 Inc. 4“.059 4O.539 4’*800 T.4/,5” 3’,15” 2’,35” T’. 6’,3 5” 5’,50” 4’,55” V. 4.039 gms. 4.451 gms. 4.743 gms. W. 281.5 , 281.3 , 282*4 , L.H. 264.0 262.4 264.6 Mean latent heat 263.7. Iodide of Methyl.-This compound was prepared by taking 50 gms. of purified wood-spirit and 10 gms. of phosphorus and adding iodine in small quantities as long as it was dissolved. The quantity of iodine taken up by the liquid was about 69 grammes. The liquid was then distilled at a temperature varying &om 70° to 90° (158O -196O F.) the distillate washed with ice-cold water and added to a large excess of chloride of calcium with which it was allowed to digest for three days. It was afterwards rectified three times from chloride of calcium. It boiled at 42O-2 (108O F.) under a pressure of 29.6 in.Specific heat assumed to be 0.158. I. 11. 111. IV. Bar. 29.71 in. 29-70 in. 29.81 in. 29.81 in. Air. 9O.50 9”-45 8”80 9’-20 Ex. 2O.06 2’*33 1”-56 1O.83 Inc. 3O.689 3”%83 3’-417 3O.761 T. 5’ 15” 4’,50’’ 4’,50” 5’,55” T’. 7’,40” 7’,20” 7‘,25” 8’,30” v. 21.465 gms. 22.446 gms 20.011 gms. 21.460 gms. I. 11. 111. IV. W. 288-0gms. 286.9 pis. 291.0 gnis. 282.0 pis. DR. ANDREWS ON THE LATENT HEAT OF VAYOUHS. L.H. 46.06 46.39 46.00 45-83 Mean latent heat 46-07. Acetate of Methyl.-The impure acetate of methyl obtained by distilling a mixture of purified wood-spirit acetate of soda and sulphuric acid was digested with milk of lime and chloride of calcium afterwards added in excess.After allowing the mixture to stand for twenty-four hours the ether was decanted and digested for several days with chloride of calcium and finally distilled in a water- bath whose temperature never exceeded 65O (149O F.). It boiled under a pressure of 30 in. at 55' (131' F.). Specific heat assumed to be 0.47. I. 11. 111. Bar. 29.77 in. 29.78 in. 29.78 in. Air. 10°~OO lO"~10 10"*60 Ex. 1'4 2O.06 1'-94 Inc. 3"*806 3O.633 3O.5 78 T. 4/,35/' 4',40/' 4',35" T'. 7/,35/( 8/,5/' 7',25" v. 8.485 gms. 8.158 pis. 8.040 pis. W. 283.8 , 284.2 , 284.1 , L.H. 110.0 110.3 110.2 Mean latent heat 110.2. Furmiate of Methyl.-It was prepared and purified by a process analogous to that last described. It boiled at 32'0.9 (91'-2 F.) under a pressure of 2'3.6 in.Specific heat assumed to be 0.47. I. IT. 111. IV. Bar. 30.07 in. 30.07 in. 30.06 in. 30.06 in. Air. 12O.70 13"-05 13'*00 13O.30 Ex. 1O-17 1'028 0°*94 lO.40 Inc. 2O.289 2O.272 f2O.417 fJ"739 T. 3',45" 3 10" 3 15" 3/,20/' T. S',5" 5' 15" 5',25/' 5/,30" V. 5.380 pis. 4.090 gnis. 5,736 gms. 6.272 gms. w. 289.0 , 291.4 , 294.5 , 282.7 ,, L.H. 116.7 116.7 117-7 117.3 Mean latent heat 117-1. I have collected the foregoing results in the following table. The first column contains the latent heat for 1 gramme of each vapour; 40 DR. ANDREWS os THE LATENT HEAT OY viwouits. the second for 1 liter taken at the temperature of the point of ebul-lition of the vapour and under the mean barometric pressure at which the experiments were performed.For 1 gramme. For 1 liter. Bromine . . 45.60 269.6 Protochloride of phosphorus 51.42 244.4 Sulphuret of carbon . 86.67 254-9 Bichloride of tin . . 30.53 253.5 Water . . 535.90 318.3 Sulphuric ether . . 90.45 268.2 Alcohol . . 202.40 324.2 Methylic alcohol . . 263.70 303.5 Iodic ether . . 46.87 254.7 Iodide of methyl . . 46.07 252% Acetic ether . . 92.68 2287.9 Acetate of methyl . . 110.20 303.6 Formic ether . . 105.30 290.3 Formiate of methyl . . 117.10 282% Oxalic ether . . 72-72 2914 It is obvious from a cursory inspection of this table that there exists some general relation between the volume of the vapour and its latent heat but many other elements would require to be taken into consideration before the precise nature of this relation can be determined.It has indeed been concluded from a comparison I believe of the latent heats of water and alcohol that the latent heat of equal volumes of different vapours is the same; but the experimental results now obtained do not support so very simple and general a relation. It is not improbable however that under certain physical conditions the proposition may be correct but until these are realized and the result established by direct experiment we cannot be justified in drawing so general a conclusion. It may be well to remark that in the above table the latent heats of equal volumes of each vapour taken at the respective boiling points of the fluids are compared; but in order to make the comparison more perfect it would have been necessary to have examined equal volumes of t,he vapours taken at the same temperature.This could not it is obvious have been done without operating under very different pressures and thus introducing another source of complication into the results. Another circumstance to which I may also refer as connected with this subject is the uncertainty that prevails as to the molecular constitution of some vapours near the tcmperatures at MR FERGUSON ON THE CHARRING ACTION OF STEAM. 41 which they condense. The recent experiments of Cahours leave it is true little doubt that the densities of the vapours of the alcohols and of most of the compound ethers correspond with theory at all temperatures but the singular anomalies presented by the acetic formic and sulphuric acids and by the perchloride of phosphorus and some essential oils show with what circumspection we must adopt the theoretical number as truly representing the density of any vapour near its point of condensation.Some of the irregularities in the results now given may perhaps be traced to this cause. Dec. 20 1847. Thomas Graham Esq. Vice-president in the chair. Professor Dana presented a copy of his memoir On certain laws of cohesive attraction,” to the Library. Messrs. Charles W. Swaisland J. C. Stevenson Henry Watts B.A. Edward Frankland William Payne Robert Galloway and W. E. Heathfield were duly elected members of the Society. The following communications were read On the power of low pressure steam in charring animal and vegetable matter and on the reducing power of charcoal at that temperature by FERGUSON, WILLIAM EsQ.-An unsound steam-engine boiler having been covered with patent felt to prevent radiation from its surface the felt was observed at the expiration of five or six months to have become charred wherever the steam made its escape through the cracks of the boiler whilst those parts of the felt which remained dry although exposed to the same heat were perfectly unaltered.The boiler was worked under a pressure of 6 lbs. which corresponds with a temperature of 232’ F. but the temperature of the escaping steam and of those parts of the felt in contact with it was 212O F. Another instance in which wood had been charred was observed in the float-gauge of a brewing-copper which had been exposed during five years to the vapour and the saccharine solution at a temperature not exceeding 215’ or 216’ F.The charcoal in this case was permeated by a soluble salt of copper and the interstices were filled with octahedral and dedocahedral crystals of metallic copper. The author concludes from the odour of pyroligneous acid which was perceptible that acetic acid was formed by the decomposition of the wood and that this united with the copper to form an acetate which even at the temperature of 216O F. was partially reduced to the metallic state whilst in intimate contact with the porous charcoal.