Library 
 
 Citrus Expei i" litl Cation 
 University ot California 
 S. DEPARTMENT OF AGRICULTURE, 
 
 BUREAU OF ANIMAL INDUSTRY. BULLETIN 124. 
 A. D. MELVIN, CHIEF OF BUREAU. 
 
 METHODS AND STANDARDS IN 
 BOMB CALORIMETRY. 
 
 INVESTIGATIONS IX COOPERATION WITH THE INSTITUTE OF 
 ANIMAL NrTKITION OF THE PENNSYLVANIA STATE COLLEGE. 
 
 i\lk Pkl IDS 
 
 
 BY 
 
 \ 
 
 CD 
 
 t-b 
 
 -2/L 
 
 ]. AUGUST FRIF.S, 
 
 Assistant /:".r/V;7 in Annual Xutrition 
 
 WASHINGTON: 
 
 GOVERNMENT PRINTING OFFICE. 
 1910.
 
 library 
 
 Citrus Experiment Station 
 
 I I ri i i/ 1, ,-. IT Jailed August 29, 1910. 
 
 Umveisity of taliforrija 
 U. S. DEPARTMENT OF AGRICULTURE, 
 
 BUREAU OF ANIMAL INDUSTRY. BULLETIN 124. 
 
 A. D. MELVIN, CHIEF OF BUREAU. 
 
 METHODS AND STANDARDS IN 
 BOMB CALORIMETRY. 
 
 INVESTIGATIONS IN COOPERATION WITH THE INSTITUTE OF 
 ANIMAL NUTRITION OF THE PENNSYLVANIA STATE COLLEGE. 
 
 BY 
 
 J. AUGUST FRIES, 
 Assistant Expert in Animal Nutrition. 
 
 WASHINGTON: 
 
 GOVERNMENT PRINTING OFFICE. 
 
 1910.
 
 THE BUREAU OF ANIMAL INDUSTRY. 
 
 Chief: A. D. MELVIN. 
 Assistant Chief: A. M. FAKRINGTON. 
 Chief Cleric: CHARLES C. CARROLL. 
 
 Animal Husbandry Division: GEORGE M. ROMMEL, chief. 
 Biochemic Division: M. DORSET, chief. 
 Dairy Division: B. H. RAWL, chiet. 
 
 Inspection Division: RICE P. STEDDOM, chief; MORRIS WOODEN, R. A. RAMSAY, 
 and ALBERT E. BEHNKE, associate chiefs. 
 Pathological Division: JOHN R. MOHLER, chief. 
 Quarantine Division: RICHARD W. HICKMAN, chief. 
 Zoological Division: B. H. RANSOM, chief. 
 Experiment Station: E. C. SCHROEDER, superintendent. 
 Editor: JAMES M. PICKENS. 
 2
 
 LETTER OF TRANSMITTAL. 
 
 U. S. DEPARTMENT OF AGRICULTURE, 
 
 BUREAU OF ANIMAL INDUSTRY, 
 
 Washington, D. C., May 5, 1910. 
 
 SIR; I have the honor to transmit and to recommend for pub- 
 lication in the bulletin series of this Bureau a manuscript entitled 
 "Methods and Standards in Bomb Calorimetry," by J. August Fries, 
 assistant expert in animal nutrition. 
 
 The investigation described is a continuation of that already 
 reported in Bulletin 94 of this Bureau, and is connected with the 
 work in animal nutrition conducted at State College, Pa., by coopera- 
 tion between the institute of animal nutrition of the Pennsylvania 
 State College and this Bureau through its Animal Husbandry Divi- 
 sion. The particular objects sought to be attained by Mr. Fries in the 
 present paper are set forth in the accompanying letter of Doctor 
 Armsby, the expert in direct charge of the cooperative investigations. 
 Respectfully, 
 
 A. D. MELVIN, 
 
 Chief of Bureau. 
 Hon. JAMES WILSON, 
 
 Secretary of Agriculture.
 
 LETTER OF SUBMITTAL. 
 
 STATE COLLEGE, PA., October 20, 1909. 
 
 SIR: 'I have the honor to submit herewith the results of experi- 
 ments by Mr. J. August Fries, M. S., assistant expert in animal nutri- 
 tion, upon "Methods and Standards in Bomb Calorimetry." 
 
 The accurate determination of the heats of combustion of organic 
 substances is not only a fundamental requirement in the nutrition 
 investigations now being conducted in cooperation with the insti- 
 tute of animal nutrition of the Pennsylvania State College, but is of 
 great importance in many other lines of both scientific and technolog- 
 ical research. Mr. Fries's investigations are a continuation of those 
 reported in Bulletin 94 of the Bureau of Animal Industry and deal 
 essentially with the standardization of methods as a means of secur- 
 ing results which shall be comparable among themselves and bear a 
 definite relation to established physical constants. To this end a new 
 method of determining the hydrothermal equivalent of the bomb 
 calorimeter has been devised; the influence of impurities in the oxy- 
 gen used, as well as of some other minor sources of error, has been 
 studied; and a redetermination of the heat of combustion of benzoic 
 acid has been made with reference to its acceptance as a standard 
 substance in bomb calorimetry. 
 
 It is believed that the results of these investigations will be of 
 interest and value to all experimenters who use the bomb calorimeter 
 for any purpose. 
 
 Very respectfully, HENRY PRENTISS ARMSBY, 
 
 Expert in Animal Nutrition. 
 
 Dr. A. D. MELVIN, 
 
 Chief of the Bureau of Animal Industry. 
 4
 
 CONTENTS* 
 
 Page. 
 
 Introduction 7 
 
 Hydrothermal equivalent of the calorimeter 7 
 
 Necessity of a common standard 8 
 
 Determination of the water value of the bomb calorimeter 8 
 
 By computation of component parts 9 
 
 The electric method 10 
 
 Error due to evaporation of water 14 
 
 A third method 19 
 
 Displacement of water 19 
 
 Water value of the calorimeter 21 
 
 Correction for combustible gases in the oxygen 22 
 
 Nature of combustible gases 26 
 
 The heat of combustion of benzoic acid 26 
 
 Sulphur, phosphorus, and chlorin 28 
 
 Correction for specific heat of water 28 
 
 Change in the bomb contents 28 
 
 Change of pressure in the bomb 30 
 
 Use of the bomb calorimeter under different conditions 31 
 
 Corrections for impurities in oxygen 32 
 
 Benzoic acid as a standard 32 
 
 5
 
 Citrus Lx K i,i,, e ,,t Station 
 University of California 
 
 METHODS AND STANDARDS IN BOMB CALORIMETRY. 
 
 INTRODUCTION. 
 
 The bomb calorimeter not only is coming more and more into use 
 in research and instruction laboratories, but has also found large 
 practical application in fuel-testing laboratories, and is beginning to 
 find a place of usefulness as a method of chemical analysis. With 
 this increase in bomb-calorimeter work, and consequently increased 
 publication of results, one fact has been brought out very clearly, 
 namely, that there is at present great lack of uniformity in the work. 
 Reports of the work done in these various kinds of laboratories, by 
 differently trained men using different types of bomb calorimeters, 
 seem to indicate that calorimetry, instead of becoming more per- 
 fected and reliable by wider application, is in a sense becoming more 
 chaotic. One man's work can not readily be compared with that of 
 another. A calorie, in other words, is not a definite fixed quantity, 
 as it should be in bomb-calorimeter work, since no two persons neces- 
 sarily agree concerning what standard to use. 
 
 HYDROTHERMAL EQUIVALENT OF THE CALORIMETER. 
 
 Each individual bomb calorimeter must have its hydrothermal 
 equivalent, or water value, determined; that is, the number of calo- 
 ries required to raise the mass of water and metal one degree Centi- 
 grade. Preferably, this should be done at the place where it is to be 
 used, and by the individual who is to be responsible for the work. 
 For this purpose it is customary to burn substances like benzoic 
 acid, naphthalin, camphor, cellulose, sugar, etc. of known chemical 
 composition, which as a rule burn readily, can easily be obtained in a 
 high state of purity, and whose heats of combustion are supposed to 
 be known. As to the choice of a substance against which to stand- 
 ardize the apparatus, however, the investigators or operators do not 
 agree, each selecting according to his own fancy and convenience, or 
 as influenced by some one else. Thus, some may use several sub- 
 stances while others choose only one. One set of analysts use naph- 
 thalin and give it a heat value of 9,628 calories per gram, while others 
 using the same substance give it a heat value of 9,696 calories per 
 gram. Some use benzoic acid, accepting 6,322 calories per gram as 
 its heat of combustion value, while others regard this as too low, and 
 
 7
 
 8 METHODS AND STANDAKDS IN BOMB CALOEIMETRY. 
 
 use 6,335 or some other number of calories as the correct value for the 
 standard on which their work is based. Such cases could be multi- 
 plied. Each man for himself, apparently, is the condition. 
 
 NECESSITY OF A COMMON STANDARD. 
 
 Now, if work of this nature is to reach its greatest usefulness that 
 is, if the work of each individual is to be relied upon to mean a defi- 
 nite thing and thus be of use to everybody else interested in the same 
 line of work then we need above all things one common standard. 
 The writer believes that it is high time that some single substance be 
 chosen, a heat value agreed upon, and that substance in some way 
 recognized as a standard for bomb-calorimeter work. In the future, 
 should the heat value of such a substance have to be slightly changed, 
 results would still be useful and comparable after a little calculation. 
 
 From his own personal experience with the substances mentioned, 
 the writer believes that benzoic acid meets the requirements for a 
 standard better than any of the other substances, and considers it 
 the most suitable that could be selected for such a standard. It was, 
 therefore, for the purpose of calling attention to existing conditions 
 and with the hope of perchance being able to do something which 
 should help to bring to pass in the near future the adoption of such a 
 standard that a redetermination of the heat of combustion of benzoic 
 acid was undertaken. 
 
 The plan of the undertaking was to determine again the heat of 
 combustion of benzoic acid, independently of all previous determina- 
 tions of the heat of combustion of any organic substance whatsoever, 
 using an improved bomb, calorimeter recently described. The 
 problem itself, which it was desired to work out step by step, with 
 reference to the material and apparatus on hand, can be stated as 
 follows : 
 
 Having a new bomb calorimeter of unknown hydrothermal equiva- 
 lent, or water value, also an oxygen supply of undetermined correc- 
 tion for any combustible gases which may be present as impurity, 
 and assuming that no organic substance exists which has had its heat 
 of combustion accurately determined so as to be referred to or 
 accepted as a standard; to determine the heat of combustion of 
 benzoic acid. 
 
 DETERMINATION OF THE WATER VALUE OF THE BOMB CALO- 
 RIMETER. 
 
 The first requirement in order to solve the problem before us is to 
 determine the water equivalent of the whole bomb-calorimeter sys- 
 tem, assuming also that no substance with a known heat of combus- 
 tion value was to be had. In order to determine this water value of 
 
 a The Journal of the American Chemical Society, Vol. XXI, p. 272, 1908.
 
 DETERMINATION OF WATER VALUE. 9 
 
 the apparatus two known methods, one of which at least is frequently 
 referred to in connection with the bomb calorimeter, were used, and 
 also a third method devised by the writer. 
 
 BY COMPUTATION OF COMPONENT PARTS. 
 
 The first and more commonly used of the two known methods con- 
 sists in computing from the weight of each of the component parts of 
 the bomb system and the corresponding specific heats the water value 
 of each substance, the sum of all giving the water equivalent of the 
 whole system or apparatus. This method is not necessarily abso- 
 lutely correct, since the weight of some of the parts can only be 
 known approximately, as, for instance, the glass and mercury of the 
 thermometer, small rubber pieces, etc., which can not be discon- 
 nected or weighed. Further, the specific heat of the particular steel 
 used for the bomb itself has not been determined, nor is it certain 
 that the other specific heats are all absolutely correct. However, 
 while we can not claim absolute correctness for this method, the total 
 value obtained for the whole system, including the water, need not 
 vary more than a few hundredths, or at most a very few tenths, of 1 
 per cent from the true water value. 
 
 The apparatus in question was an Atwater-Hempel bomb calori- 
 meter, having the top modified so as to permit the determination 
 of the carbon dioxid after a combustion. The modification consists 
 in having, besides the usual valve and opening for the intake of 
 oxygen, an outlet terminating in a platinum tube near the bottom of 
 the bomb and through which the gases are removed for analysis. 
 
 From the weight of each of its different parts and their respective 
 specific heats, the following water value for the bomb calorimeter 
 system was obtained: 
 
 TABLE 1. Computed water value of bomb calorimeter. 
 
 Material. Weight. 
 
 Specific Water 
 heats. equivalent. 
 
 Grams. 
 Steel 3,230.0 
 
 Grams. 
 oQ.1114 300 49 
 
 Platinum 1%. 
 
 a. 0320 . 27 
 
 Lead ...... 66. 
 
 a 0300 98 
 
 German silver (approximate) . 4.0 
 
 a.0940 ; .38 
 
 Rubber (approximate) 4.0 
 
 6. 3310 . 32 
 
 Iron (approximate) 10.0 
 
 a.1114 11 
 
 Mercury (approximate) 50.0 
 
 o.0330 .65 
 
 Glass (approximate) 10. 
 
 0.1900 .90 
 
 Britannia metal. . 855.0 
 
 a. 0548 46.85 
 
 Oxygen (constant volume) 11.4 
 
 a. 1570 1.79 
 
 Water at 22 C 2,000.0 
 
 f.9975 1,995.00 
 
 
 
 Total 
 
 2,418.74 
 
 
 
 a The Journal of the American Chemical Society. Vol. XXV, p. (194. 1903. 
 
 bll. W. Wiley. Principles and Practice of Agricultural Analysis. Vol. Ill, p. 573. 
 
 < Annalen der Physik. ser. 4, 16, 010 (1905.) 
 
 44865 Bull. 12410 2
 
 10 METHODS AND STANDARDS IN BOMB CALOKIMETRY. 
 
 Except in the cases of rubber and water, the specific heats used in 
 the above computation are those used by Atwater in determining 
 the water value of his bomb calorimeter. For the small quantity of 
 iron in the connectors the same specific heat is used as for the steel. 
 The specific heat of water is the average result of Dieterici and 
 Barnes's determinations. 
 
 According to Table 1, the total water equivalent of the whole 
 bomb-calorimeter system, including the water, is 2,418.74, or without 
 the water it is 423.74. Should the other value given by Atwater for 
 steel (0.1087 specific heat) be used, the water equivalent would be 
 415, or 2,410 including the water. The water in which the bomb 
 is immersed and through which the heat is measured should always 
 be the same in amount in order to insure the same water level 
 in the cylinder, thus keeping the conditions unchanged. With this 
 apparatus 2,000 grams of water will immerse the bomb completely, 
 and is the quantity which was uniformly employed. 
 
 THE ELECTRIC METHOD. 
 
 The second method employed in determining the water equivalent 
 consisted in generating a measured amount of heat in the bomb by 
 means of an electric current passing through a resistance coil. The 
 generation of heat in the bomb and the measurement of the rise in 
 temperature due to it were done under the same conditions as when 
 a substance is burned for its energy determination, except that no 
 oxygen was introduced into the bomb. Correction, therefore, must 
 be made for the usual amount of oxygen in computing the results. 
 
 The test was made in the following manner: About 10 inches of 
 size 26 B. & S. = 0.016 "nichrome" resistance wire was made into a 
 small coil which was connected to the two platinum wires in the 
 bomb in such a manner that the heat would be generated at about 
 the same place as where the substances analyzed are burned. The 
 resistance of this wire coil was about 1.38 ohms. Next, the bomb 
 was closed, placed in the water, and connected up as for a determina- 
 tion of heat of combustion, and the two insulated copper wires lead- 
 ing from the bomb were connected to the electrical instrument. The 
 electric current was supplied by six storage cells and was measured 
 by voltmeter and ammeter. After starting the stirrer and taking 
 the usual few minutes preliminary readings of the water tempera- 
 tures, the switch was closed at a given signal and the current from 
 the six cells sent through the bomb. It was allowed to flow through 
 for a number of minutes, the readings of the voltmeter and ammeter 
 being taken every half minute. The water temperature was taken 
 every minute by means of a Beckman thermometer read to 0.001 C. 
 During the first few trials the voltmeter and ammeter used were the
 
 ELECTRIC METHOD OF DETERMINING WATER VALUE. 
 
 11 
 
 commercial, so-called American, instruments, the ammeter having an 
 external shunt. 
 
 The various observations noted during one of these trials in which 
 the electric current was on continuously for 12 minutes are found 
 in Table 2. 
 
 TABLE 2. Electric determination of voter equivalent. 
 
 Period. 
 
 Time. 
 
 Temperature of calo- 
 rimeter. 
 
 Voltmeter. 
 
 Ammeter. 
 
 As read. 
 
 Corrected. 
 
 Preliminary. ... 
 
 Minutes. 
 1.0 
 2.0 
 3.0 
 4.0 
 5.0 
 
 C. 
 1.236 
 1.239 
 1.244 
 1.247 
 1.252 
 
 C. 
 1.2432 
 
 Volts. 
 
 A mperes. 
 
 Current on 
 
 
 
 
 
 1.2592 
 
 
 
 5.5 
 
 
 11.68 
 11.62 
 11.60 
 11.60 
 11.59 
 11.59 
 11.58 
 11.58 
 11.58 
 11.58 
 11.58 
 11.58 
 11.58 
 11.58 
 11.58 
 11.58 
 11.58 
 11.58 
 11.58 
 11.58 
 11.58 
 11.58 
 11.58 
 11.58 
 
 4.62 
 4.60 
 4.60 
 4.60 
 4.58 
 4.58 
 4.58 
 4.58 
 4.60 
 4.60 
 4.60 
 4.60 
 4.60 
 4.60 
 4.60 
 4.60 
 4.60 
 4.60 
 4.60 
 4.60 
 4.60 
 4.60 
 4.60 
 4.60 
 
 Equalizing 
 
 6.0 
 6.5 
 7.0 
 7.5 
 8.0 
 8.5 
 9.0 
 9.5 
 10.0 
 10.5 
 11.0 
 11.5 
 12.0 
 12.5 
 13.0 
 13.5 
 14.0 
 14.5 
 15.0 
 15.5 
 16.0 
 16.5 
 17.0 
 
 1.370 
 
 1.3781 
 
 1.660 
 
 1.6696 
 
 1.970 
 
 1.9807 
 
 2.280 
 
 2.2918 
 
 2.595 
 
 2.6084 
 
 2.910 
 
 2.9240 
 
 3.225 
 
 3.2385 
 
 3.545 
 
 3.5567 
 
 3.845 
 
 3.8564 
 
 4.155 
 
 4.1667 
 
 4.470 
 
 4.4816 
 
 4.780 
 
 4.7914 
 
 18.0 4.974 
 19.0 5.005 
 20. 5. 008 
 21.0 i 5.009 
 
 4.98(10 
 5.0170 
 5.0200 
 5.0210 
 
 
 
 End period 
 
 
 
 
 
 22.0 5.006 
 23.0 5.004 
 24. 5. 001 
 25. 4. 998 
 
 
 
 
 
 
 
 
 5.0100 
 
 
 
 The ammeter used had an initial correction of 0.16, which has to 
 be added to the average of the readings. Accordingly, the average 
 for the current was: 
 
 For total time, 11.588 volts, 4.757 amperes; for last 8 minutes, 11.58 volts. 
 
 4.76 amperes. 
 Room temperature, 24 C. 
 Temperature of water at beginning, 21.2 C. 
 Temperature of water at end, 25.0 
 
 Most of the figures found in the second column of Table '2 wore 
 read when the mercury column in the thermometer was moving 
 rather fast, hence a error of ono or two thousandths of a degree 
 could readily be made, but any error of that kind is reduced to a
 
 12 METHODS AND STANDAEDS IN BOMB CALORIMETRY. 
 
 minimum by the number of readings taken. If we examine the 
 table, we notice that from about the third minute there was a uniform 
 increase in temperature of the bomb system, while the voltmeter 
 and ammeter remained unchanged, indicating a constant current. 
 Because of this constancy, as regards both the current and the rise 
 in temperature of the calorimeter, the results of the test can be 
 worked out either from the total rise in temperature and total heat 
 generated, or from a section of the time consisting of the last 8 or 9 
 minutes. 
 
 The radiation correction, or correction due to the influence of the 
 surrounding air conditions, in the case of the electric tests, as well as 
 in all the following determinations of heats of combustion, has been 
 worked out by using the Regnault-Pfaundler formula a 
 
 v-v'/n-l , dn + 6, 
 
 y = sum of readings minus 1 increased by an arbitrary factor 2 * 
 
 v= average rate of radiation during preliminary period. 
 v' = average rate of radiation during end period. 
 6n = number of readings during combustion period. 
 t = average of preliminary thermometer readings. 
 t' = average of end period thermometer readings. 
 Applying the correction thus found to the entire test represented 
 by Table 2, we have: 
 
 Last reading of the heating period ........................... +5. 0210 
 
 First reading of the heating period ........................... 1. 2592 
 
 Radiation correction ........................................ . 0029 
 
 Correction for thermometer lag ............................... . 0010 
 
 Total rise in temperature .............................. 3. 7579 
 
 If we take a section consisting of the last 8 minutes of the test, 
 and represent by means of a curve the gain and loss to the system 
 by radiation, we obtain a correction of +0.0013 C. and a correction 
 for thermometer lag of 0.0005 C. Applying these corrections to 
 
 the last 8 minutes, we have: 
 
 c 
 Thermometer reading for the twelfth minute ................ +4. 7914 
 
 Thermometer reading for the fourth minute ................. 2. 2918 
 
 Radiation correction ........................................ + . 0013 
 
 Correction for thermometer lag ............................. . 0005 
 
 Corrected rise for 8 minutes ............................ 2. 5004 
 
 In computing the heat generated in the bomb by the electric cur- 
 rent and the corresponding water equivalent of the apparatus the 
 
 a H. W. Wiley. Principles and Practice of Agricultural Analysis. 1897. Vol. 
 Ill, p. 572.
 
 ELECTRIC METHOD OF DETERMINING WATER VALUE. 
 
 13 
 
 mean small calorie is used, that is, one one-hundredth of the heat 
 required to heat 1 gram of water from to 100 C., equivalent to 
 4.1834 Joules. The electrical energy developed in the bomb and 
 measured as heat would then be expressed in calories by the following 
 formula : 
 
 ni _ volts x amperes X seconds 
 4.1834" 
 
 During the 12 minutes, or 720 seconds, we had the following amount 
 of heat evolved in the bomb: 
 
 1 1 .588 X 4.757 X 720 H- 4.1834 = 9,487.4 calories, 
 and 
 
 9,487.4 calories -T- 3. 7579 rise = 2, 524. 7 grams water equivalent. 
 
 At the time of the test there was no oxygen in the bomb; hence 
 a correction for the amount usually present in the bomb must be 
 applied. The amount of oxygen in this bomb at 20 atmospheres 
 pressure equals 10.24 grams, which, multiplied by 0.157 the specific 
 heat of oxygen at constant volume equals 1.6 grams water, wliich 
 must be added to the results found for the whole system, giving 
 2,524.7 + 1.6 = 2,526.3 grams as the water equivalent. 
 
 For the 8-minute section referred to we have : 
 11.580 X 4.76 X 480-^4.1834 = 6,324.5 calories, 
 and 
 
 6,324.5 -=-2.5004 = 2,529.3 grams. Adding 1 .6 for the oxygen to it gives 
 a water equivalent of 2,530.9. 
 
 Two other tests with the same instruments were made, one having 
 the current on for 10 minutes and the other for 12 minutes, and 
 worked out in the manner already described, the results of the three 
 tests being given in Table 3 below. 
 
 TABLE 3. Water equivalent of calorimeter by three electric tests. 
 
 Test. 
 
 
 Heat 
 evolved in 
 the bomh. 
 
 Corrected 
 rise in tem- 
 perature. 
 
 Water 
 equivalent. 
 
 Correction 
 for O s . 
 
 Water 
 equivalent 
 corrected. 
 
 
 Time. 
 /Total 12 minutes 
 
 Calories. 
 9, 487. 4 
 
 3. 7579 
 
 Grams. 
 2,524 7 
 
 Grams. 
 I 
 
 Grams. 
 2 52ti 3 
 
 1 
 
 (Last 8 minutes 
 
 ti 324 5 
 
 2 5004 
 
 2 5'>9 3 
 
 1 ti 
 
 2 530 9 
 
 
 (Total 10 minutes 
 
 7 969 ti 
 
 3 1374 
 
 2 540 1 
 
 1 ti 
 
 2 541 7 
 
 2 
 
 \Last 6 minutes 
 
 4,759 2 
 
 1 8885 
 
 2 520 1 
 
 1 6 
 
 '' 5''1 7 
 
 
 (Total 12 minutes.. . 
 
 9,48<i. 9 
 
 3 7003 
 
 2 522 9 
 
 1 ti 
 
 2 524 5 
 
 3 
 
 \Last8minutes 
 
 (1,313.0 
 
 2. 4910 
 
 2,534 3 
 
 1 ti 
 
 2 535.9 
 
 
 
 
 
 
 
 
 The average water value of the three tests obtained when the total 
 heat is used is equivalent to 2,530.8 grams of water, and when the 
 effect of the last 8 and 6 minutes of the electric current is considered, 
 the average water value is equal to 2,529.5 grams. 
 
 a A. W. Smith. Monthly Weather Review for October, 1907, p. 11.
 
 14 
 
 METHODS AND STANDARDS IN BOMB CALORIMETKY. 
 
 These results are about 4.6 per cent higher than that calculated from 
 the weights and specific heats of the material of the bomb. Among 
 themselves, the results agree fairly well, an indication that the source 
 of error, if any exists, must be a constant one. Suspicion fell upon 
 the ammeter, which already had an initial error of +0.16 ampere, and 
 the possibility of electrolytic action upon the" water. Another 
 ammeter was used, this time a Weston' instrument, and a piece of 
 rubber tubing was slipped over the metal connector so as to have no 
 metal in direct contact with the water. Two tests were made under 
 these conditions, the electric current being on for 12 minutes in each 
 case. 
 
 Without reproducing the readings of the instruments, etc., the 
 total heat as well as the heat evolved in the bomb during the last 
 9 minutes, the corresponding rise in temperature, and the water 
 equivalent of the bomb system are shown in Table 4. 
 
 TABLE 4. Water equivalent of calorimeter by two electric tests. 
 
 Test. 
 
 
 Heat 
 evolved in 
 the bomb. 
 
 Corrected 
 rise in tem- 
 perature. 
 
 Water 
 equivalent. 
 
 Correction 
 for O 2 . 
 
 Water 
 equivalent 
 corrected. 
 
 
 Time. 
 /Total 12 minutes 
 
 Calories. 
 9 125.5 
 
 C. 
 3. 6985 
 
 Grams. 
 2,467.3 
 
 Grams. 
 1.6 
 
 Grams. 
 2, 468. 9 
 
 1 
 
 \Last 9 minutes '. . 
 
 6, 828. 7 
 
 2. 7550 
 
 2,478.6 
 
 1.6 
 
 2,480.2 
 
 
 (Total 12 minutes 
 
 9,066.1 
 
 3. 6710 
 
 2,469.6 
 
 1.6 
 
 2,471.2 
 
 2 
 
 \Last 9 minutes 
 
 6,790 5 
 
 2, 7445 
 
 2 474.2 
 
 1.6 
 
 2, 475. 8 
 
 
 
 
 
 
 
 
 With instruments of this kind where the hundredth part of an 
 ampere or volt has to be estimated it can not be claimed nor expected 
 that the results should be reliable to within 0.5 per cent. The 
 average of the above water equivalents equals 2,474 grams, which 
 is still over 2 per cent above that computed from the specific heats. 
 It was therefore decided to test one more possible source of error, 
 viz, the evaporation of water from the system under the existing 
 laboratory conditions. 
 
 ERROR DUE TO EVAPORATION OP WATER. 
 
 The evaporation from the surface of the water in the cylinder con- 
 taining the bomb is held to be of so little consequence that it is gen- 
 erally entirely neglected, but the writer made a few tests in order to 
 get results which should apply to this apparatus, locality, and labo- 
 ratory. In the Atwater-Hempel bomb calorimeter the water cylin- 
 der is surrounded by two separate dead-air spaces, and the two covers 
 for these spaces are of smooth hard rubber. These covers fit snugly, 
 so that practically there can be no currents in the inclosed air. 
 
 The tests were made in the following manner: The water cylinder 
 was filled with water to the same level as when the bomb is in place. 
 The stirrer was placed in the water, and to represent the two rubber-
 
 ERROR DUE TO EVAPORATTOX OF WATER. 
 
 15 
 
 covered connecting wires for the electric current, two similar small 
 pieces of rubber-covered wire were suspended from the edge of the 
 vessel dipping into the water. The cylinder was then weighed to 0.01 
 gram and the exact time noted. It was then quickly put in its place 
 and the stirrer operated as during a combustion for from 15 to 30 
 minutes. The time of starting and stopping the stirrer, as well as 
 the time of weighing, was noted. 
 
 These evaporation tests were carried on in the calorimeter both 
 with the stirrer in operation and with the stirrer standing undisturbed, 
 but covered. The water was also left standing exposed to the air of 
 the laboratory in a place where there was no draft. Standing exposed 
 in the laboratory, the average of several trials was 0.0193 gram of 
 water evaporated per minute, whereas standing covered in the bomb 
 calorimeter the evaporation was only 0.0034 gram per minute. 
 When the stirrer was in operation, the evaporation increased. Below 
 are given the details of one of the trials: 
 
 TABLE 5. Evaporation of water from calorimeter. 
 
 Items. 
 
 Time. 
 
 Weight of ves- 
 sel + water, 
 stirrer, etc. 
 
 Stirrer started .. 
 
 9.40 a. m 
 
 Grams. 
 
 
 10. 10 a. m 
 
 
 
 
 
 Difference . 
 
 30 minutes. 
 
 
 
 
 
 Weight before taken * 
 
 9. 3X a. m 
 
 3 COO 5(> 
 
 Weight after taken . 
 
 10. 13 a. m. 
 
 3.600. 12 
 
 
 
 
 Difference 
 
 35 minules 
 
 44 
 
 
 
 
 Temperature of room, 21 C. 
 Temperature of water, 21 C. 
 Time of stirring the water, 30 minutes. 
 Time required for handling, 5 minutes. 
 Correction for 5 minutes, 5X0.0193=0.097 gram H,0. 
 
 0.440.097=0.343 gram evaporated during 30 minutes, or 0.0114 gram per 
 minute. 
 
 Ten trials showed the following rates of evaporation per minute: 
 
 Gram. 
 No. 1 . . . 0. 00<J7 
 
 No. 2... 
 No. 3... 
 No. 4... 
 No. 5... 
 No. 6... 
 No. 7... 
 No. 8... 
 No. 9... 
 
 0113 
 
 0075 
 
 0122 
 
 0114 
 
 0085 
 
 0107 
 
 0044 
 
 0048 
 
 No. 10... .0075 
 
 Average 0085
 
 16 METHODS AND STANDARDS IN BOMB CALORIMETRY. 
 
 These tests were made between November 30 and January 17. 
 
 The above evaporation, though small, makes a correction which 
 should not be neglected, especially when small charges are used, or 
 charges in any way differing from the quantity used in the stand- 
 ardization of the apparatus. The heat of water at 21 C. is, accord- 
 ing to Prof. A. W. Smith, equal to 585.26 mean calories for 1 gram 
 of water. 
 
 If we apply the above correction to the last-mentioned electric 
 tests (Table 4) it would be 16 6 minutes X 0.008 gram H 2 O = 0.128 
 gram H 2 O and 0.128x585.26 = 74.93 calories to be subtracted from 
 the calories given in the first column opposite the total for 12 minutes. 
 For the 9 minutes section the correction would be 9 X 0.008 = 0.072 
 gram H 2 O, and 0.072x585.26 = 42.14 calories. Recalculating, the 
 four water values would be: 
 
 2, 447. 09 
 2, 463. 36 
 2, 449. 24 
 2, 458. 87 
 
 Average=2, 454. 64 
 
 This corrected average water value is still over 1.3 per cent greater 
 than that computed according to the first method, and the difference 
 is undoubtedly too large to be ascribed to the manipulation or reading 
 of the instrument. In all probability some electrolysis of water 
 must have taken place in spite of the precaution taken, and we can 
 not be sure on this point, since the connection was not dry. Any 
 error due to condensation of moisture on the outside of the water 
 vessel, and subsequent evaporation of the same, has not been ob- 
 served and can at best be but small. 
 
 The evaporation tests may throw some light upon this problem of 
 condensation, etc. The inner air space or layer of air which sur- 
 rounds the water cylinder in the calorimeter equals about 4 liters. 
 At 22 C. these 4 liters of air when saturated would contain 0.0772 
 gram of water. In about 9 minutes, therefore, perfectly dry air 
 should become fully saturated and the evaporation cease. This is 
 not the case. The tests showed that the evaporation continued 
 unchecked, and in the particular test already referred to there was a 
 loss of 0.343 gram of water in 30 minutes, enough water to saturate 
 17.8 liters of dry air. But since the air in the calorimeter laboratory 
 always contains some moisture, in reality a much larger volume of 
 air would be saturated. The fiber envelope is supposed to be water- 
 proof, and hence it is very unlikely that the water vapor is absorbed. 
 It would seem that the water vapor which is produced at the surface 
 of the water, near the cover, escapes to the outside by means of its 
 
 Physical Review, Vol. XXV, No. 3, Sept., 1907, p. 170. 
 
 &This refers to the total time influenced by the evaporation of water when the total 
 heat generated during the full time of 12 minutes is considered.
 
 EKKOR DUE TO EVAPORATION OF WATER. 17 
 
 own pressure through the openings in and around the cover. This 
 unchecked evaporation and free escape of the vapor seems to indicate 
 that the inclosed air need not necessarily be affected much, except at 
 the very top, and that the air layer around the water cylinder is 
 slowly changed by diffusion and convection currents. 
 
 A direct test, by a wet and a dry bulb thermometer, which were 
 6.0 C. apart when standing quietly in the laboratory, showed that 
 there was no effect whatever upon the moisture conditions in the air 
 space during 10 minutes' operation of the bomb. These thermom- 
 eters, bulbs one-third down in the space, stood 3.0 C. apart and 
 remained so; hence there could be no condensation of moisture on 
 the sides of the vessel. 
 
 If, now, the water cylinder as it is placed in position is a little (say 
 0.5 to 1 C.) colder than the air surrounding it, and the air is saturated 
 with moisture, condensation would begin, but the conditions in the 
 bomb room have never at the time of making a combustion been 
 such that a condensation would have taken place at the start with 
 only one degree difference in temperature. The water cylinder is in 
 the calorimeter only a few minutes, as a rule, before the substance is 
 ignited, and it is questionable if in that length of time the conditions 
 of the air have changed enough so that a condensation can take place, 
 except, perhaps, at the upper rim of the vessel. In less than a minute 
 after ignition, the temperature of the w T ater is higher than that of the 
 surrounding air, and hence evaporation of any water which had been 
 condensed on the vessel before the ignition took place would begin. 
 Whether any condensation or evaporation does take place has not 
 been experimentally demonstrated, but from the very nature of the 
 existing conditions at this place, errors due to them may be assumed 
 to be entirely negligible. 
 
 As a check on these evaporation results, on a clear bright day a 
 special test was made as follows: The water cylinder, filled with 
 water to within one-half inch of the top, was placed in position in the 
 calorimeter container, as during an energy determination, but with- 
 out the stirrer. The covers were put on as before and the cylinder 
 was allowed to stand for 20 minutes. It was taken out and reweighed 
 quickly, and put back the second time for 20 minutes. After that it 
 was allowed to stand in the laboratory for 24 minutes before being 
 weighed, another weight being taken S*ininutes later. During this 
 laboratory test the windows and doors were closed so that there was 
 no draft to influence the evaporation. Next, a piece of paraffined 
 paper was fitted over the top of the water cylinder and sealed by 
 means of melted soft wax. The cylinder was weighed and put in 
 position in the calorimeter container as before and reweighed after 20 
 minutes. After that it was allowed to stand in the laboratory and
 
 18 
 
 METHODS AND STANDARDS IN BOMB CALORIMETEY. 
 
 was weighed after different intervals. The results are as given in 
 Table 6. 
 
 TABLE G. Evaporation tests. 
 
 Method. 
 
 Water cylinder. 
 
 Evaporation per 
 minute. 
 
 Time 
 weighed. 
 
 Weight. 
 
 Time 
 placed in 
 position 
 and 
 removed. 
 
 In labora- 
 tory. 
 
 In bomb 
 room. 
 
 CYLINDER UNCOVERED. 
 
 9.14 a. m 
 
 Grams. 
 3, 480. 43 
 
 9.15 a. m 
 
 Gram HO. 
 
 Gram H Z O. 
 0.0035 
 
 Difference 
 
 9.3CU a. m... 
 
 3,480.32 
 
 9.35 a. m. . 
 
 22J mins 
 
 .11 
 
 20 mins. .. 
 
 
 9.36A a. m 
 
 3, 480. 32 
 3.480.21 
 
 9.37 i a. m. 
 9.57J a. m. 
 
 Difference 
 
 9.58 a. m 
 
 21J mins .11 
 
 20 mins. .. 
 
 Average . 
 
 
 
 
 Laboratory, first trial 
 
 9.58 a. m.. 
 
 3.4X0.21 
 
 
 0. 0197 
 0.0000 
 
 Difference 
 
 10.22 a. m 3,479.71 
 
 
 
 
 24 mins . . . 
 
 .50 
 
 
 Laboratory, second trial 
 
 
 
 10.22 a. m 
 
 3,479.71 
 
 
 
 10.30 a. m... 
 
 3, 479. 58 
 
 
 
 8 mins 
 
 ,13 
 
 
 A verage 
 
 
 
 
 
 
 CYLINDER SEALED. 
 
 Bomb room 10.37 n. m 
 
 3,483.80 
 
 
 
 10.59 a. m 
 
 3. 483. 80 
 
 
 
 
 
 22 mins 
 
 0.00 
 
 
 
 
 
 10.59 a. m 
 
 3, 483. 80 
 
 
 
 0.0000 
 
 Difference. . 
 
 11.29 a. m 
 
 3, 483. 86 
 
 
 
 
 
 30 mins 
 
 0.00 
 
 
 Laboratory, second trial 
 
 
 11.29 a. m 
 
 3, 483. 8G 
 3,483.87 
 
 
 Difference 
 
 2.46 p. m 
 
 
 
 
 
 197 mins. . .. 
 
 + .01 
 
 
 Average 
 
 
 
 
 
 
 
 
 
 From this test we see that the change in weight of the water cylin- 
 der in the previous tests was due entirely to evaporation from the 
 surface of the liquid water, and that there was no condensation on the 
 sides of the cylinder or evaporation of any condensed moisture. 
 During the test the temperature of the bomb room was 24 C., and 
 the wet-bulb thermometer (having the bulb surrounded by a piece of 
 moistened filter paper and swung back and forth) registered 16 C. 
 The temperature of the water was 24 C., and in the laboratory the 
 dry thermometer registered 26.5 C., and the wet-bulb thermometer 
 16 C. 
 
 The water equivalent of the bomb as determined by the electrical 
 tests which have been described is not satisfactory, but the tests
 
 NEW METHOD FOE DETERMINING WATER VALUE. 19 
 
 have, nevertheless, been useful and seem to justify the following 
 conclusions : 
 
 1. The tendency of the electric method is to give results that are 
 too high. 
 
 2. There are many chances for error connected with an electric 
 test, even if the instruments used have been carefully calibrated. 
 
 3. Instruments which can be read to the hundredth part of an 
 ampere and volt only by estimation are not accurate enough for the 
 best work. 
 
 4. There is a possibility of electrolysis of water; hence the con- 
 nection to the one wire in the bomb should not only be insulated from 
 the metal of the bomb, but thoroughly insulated from the water 
 surrounding the bomb as well. 
 
 5. The tests led to a more thorough investigation of the error due 
 to evaporation of water during a bomb combustion, showing that 
 under usual laboratory conditions there is an error which must be 
 taken into account, at least when less or more heat is generated in 
 the bomb than was generated at the time of its standardization. 
 
 A THIRD METHOD. 
 
 The uncertainty of the foregoing results prompted the working out 
 of a simple and perfectly reliable method for the determination of the 
 water equivalent of the calorimeter. 
 
 The principle of this method consists in burning equal charges of a 
 substance in the bomb, first, under exactly the same conditions as 
 when a heat determination is made, and, secondly, after having, with- 
 out changing any of the external conditions, such as level of water, 
 etc., reduced the water equivalent of the system. The same amount 
 of oxygen is used in each case. From the difference in rise of 
 temperature and the difference in water equivalent it is possible to 
 determine very accurately the water value of the calorimeter. 
 
 By this method it is possible, first, to use a substance of unknown 
 or only approximately known heat of combustion and an oxygen 
 supply of unknown purity to determine the water equivalent of the 
 apparatus, and then by means of this new water equivalent and the 
 same determinations to work out accurately the heat of combustion 
 of the substance used, and also to determine the correction for impu- 
 rities in the oxygen, if any such were present. 
 
 DISPLACEMENT OK WATEH. 
 
 When the bomb and stirrer are in position in the water cylinder, 
 there is a space above the bomb and one near the bottom where part 
 of the water can be displaced, and thereby the water equivalent of the 
 system reduced. The displacement of water was effected by two
 
 20 METHODS AND STANDARDS IN BOMB CALOEIMETEY. 
 
 double-walled metal rings. The one to fit above the bomb was made 
 of sheet lead heavy enough to rest securely by its own weight. The 
 one for near the bottom of the bomb was made of sheet zinc and was 
 held in position by the bomb itself, hence it could be lighter than the 
 water displaced. These rings were so made that they did not touch 
 the sides of the water cylinder or in any way interfere with the oper- 
 ation of the stirrer or the thorough mixing of the water. The upper 
 and heavier ring contained 553.5 grams of lead and solder and 25.8 
 grams of zinc, and had a displacement of 306 grams of water. The 
 lower ring contained 86 grams of zinc and 20.9 grams of solder and 
 had a displacement of 162 grams of water. 
 
 The computed water equivalent of the metal rings was: 
 
 Lead (+solder) 574.4 gramsXO.0315 sp. heat =18.09 
 
 Zinc 111.8 gramsXO.0956 sp. heat a =10.68 
 
 Total 28. 77 
 
 During a heat of combustion determination the bomb is immersed 
 in 2,000 grams of water, which covers the highest point of the bomb 
 to a certain depth. When the metal rings were used, a quantity of 
 1,532 grams of water brought the water level to this same height. 
 To these 1,532 grams of water must be added the 28.8 grams water 
 equivalent of the metal. Thus we have a difference of 2,000 grams 
 - 1 ,560.8 = 439.2 grams of H 2 O, or 439.2 X 0.99745 = 438. 1 , in the water 
 equivalent of the calorimeter at 22.12 C., the temperature at which 
 the determinations of water value were made, without changing any 
 of the other conditions. If, now, exactly equal weights of a sub- 
 stance and fuse wire are burned, that is, if the same amount of heat 
 is generated in the bomb while it is immersed in the two different 
 quantities of water, there will be a difference in the rise of temperature, 
 and we have the necessary factors for the computation of the water 
 value. 
 
 It is, however, a tedious and difficult manipulation to press and 
 weigh out to the accuracy of 0.0001 gram a charge of dry, and per- 
 haps hygroscopic material, and it is much more convenient and just 
 as accurate to weigh out approximately equal quantities of the sub- 
 stance for each charge, and then, by one or the other of the two 
 methods of calculation to be described, to compute the water equiva- 
 lent of the apparatus. 
 
 In the following table (Table 7) are shown the results of a number 
 of combustions of about equal charges of benzoic acid made under 
 the two conditions, representing a difference of 439.2 grams of water, 
 equal to 438.1 grams water equivalent of the system at 22 C. 
 
 o Beilage zum Chemiker Kalender, 1904.
 
 DETERMINATION OF WATER VALUE. 
 
 21 
 
 TABLE 7. Rise in temperature due to burning like quantities ofbenzoic acid in the bomb, 
 with 20 atmospheres oxygen pressure, but with varying amounts of water in the apparatus, 
 there being a difference of 439-2 grams of ivater equal to 438.1 water equivalent. 
 
 
 
 
 
 Rise in 
 
 
 
 
 Water used. 
 
 Benzole 
 acid 
 burned. 
 
 Fuse wire. 
 
 IINOj 
 formed. 
 
 tempera- 
 ture (not 
 corrected 
 for evapo- 
 ration or 
 impurities 
 
 Rise in 
 tempera- 
 ture due to 
 wire and 
 HN0 3 . 
 
 Rise due 
 to l>enzoic 
 acid. 
 
 Rise due 
 tol 
 pram of 
 tienzoic 
 acid. 
 
 
 
 
 
 in oxygen). 
 
 
 
 
 Gram*. 
 
 Gram. 
 
 Calories. 
 
 Calories. 
 
 C. 
 
 " C. 
 
 C. 
 
 C. 
 
 2,000 
 
 7157 
 
 26.24 
 
 7.10 
 
 1.8837 
 
 0. 01378 
 
 1.86992 
 
 2. 61272 
 
 2000 
 
 7341 
 
 22.88 
 
 7.20 
 
 .9293 
 
 . 01244 
 
 1.91686 
 
 2.61117 
 
 2,000 . 
 
 7034 
 
 26.24 
 
 6.90 
 
 .8476 
 
 . 01370 
 
 1.83390 
 
 2. 60719 
 
 2,000 
 
 7162 
 
 23.04 
 
 6.95 
 
 .8826 
 
 . 01240 
 
 1.87020 
 
 2.61128 
 
 2,000 
 
 7110 
 
 26.56 
 
 6.95 
 
 .8726 
 
 .01386 
 
 1.85874 
 
 2. 61426 
 
 2,000 
 
 7045 
 
 23.68 
 
 6.95 
 
 .8510 
 
 .01266 
 
 1.83834 
 
 2.60943 
 
 
 
 
 
 
 
 
 
 Average . 
 
 
 
 
 
 
 
 2.61101 
 
 
 
 
 
 
 
 
 
 1,560.8 
 
 7122 
 
 26.24 
 
 8.25 
 
 2. 2937 
 
 .01741 
 
 2. 27629 
 
 3.1%1 4 
 
 1,560.8 
 
 6990 
 
 26.24 
 
 7-15 
 
 2. 2467 
 
 .01686 
 
 2. 22984 
 
 3.19004 
 
 1,560.8 
 
 7031 
 
 26.24 
 
 7.40 
 
 2. 2606 
 
 .01698 
 
 2. 24362 
 
 3. 19104 
 
 1,560.8 
 
 7028 
 
 26.24 
 
 7.&5 
 
 2.2524 
 
 . 01721 
 
 2. 23519 
 
 3.18041 
 
 Average 
 
 
 
 
 
 
 
 3. 18941 
 
 
 
 
 
 
 
 
 
 Difference in rise of temperature, 0.57840 C. 
 
 WATER VALUE OF THE CALORIMETER. 
 
 Two methods can be employed to compute the water equivalent of 
 the apparatus from the above determinations. 
 
 One method is to make use of the approximate heat of combustion 
 value of benzoic acid, compute the total heat generated by each 
 charge, the fuse wire, and the nitric acid, and from the average differ- 
 ence in rise of temperature due to a given difference in the water 
 equivalent of the calorimeter to compute the water equivalent of the 
 apparatus. The approximate heat of combustion value of the sub- 
 stance burned is computed from the combustions made under normal 
 conditions, using the computed water value for the calorimeter, i. e., 
 2,418.74 grams. The approximate heat of combustion of benzoic 
 acid computed in this way would be 6,315.3 calories per gram. 
 
 The second method consists in finding the value of the number of 
 calories represented by the fuse wire and the nitric acid of each charge 
 in terms of degrees rise in temperature, subtracting this from the 
 observed- rise in temperature, and then expressing the rise in tem- 
 perature as per gram substance burned. The water equivalent of 
 the apparatus is calculated from the average difference in the rise 
 of temperature per gram and the difference between the two water 
 equivalents. This method of computing is perhaps preferable to the 
 former, and since the corrections for the wire and the nitric acid are 
 small at best, it may be more correct in case there should be much vari- 
 ation in the size of the charges used for combustion. In Table 7 the 
 rise per 1 gram of the substance has been obtained according to this
 
 22 METHODS AND STANDARDS IN BOMB CALOKIMETRY. 
 
 method. To find the rise of temperature of the calorimeter due to 
 the burning of the wire and formation of HNO 3 , we use the calcu- 
 lated water equivalent of the apparatus, viz, 2,418.74 grams and 
 1,980.64 grams, respectively. Taking as an example the first deter- 
 mination in Table 7, we have: 
 
 2,418.74 : (26.24 + 7.10) : : 1 :X 
 X = 0.01378C. 
 
 From Table 7 we learn that 1 gram of the substance (in this case 
 benzoic acid) burned under the normal conditions caused a rise in tem- 
 perature equal to 2.61101 C. and burned when the water equiva- 
 lent was reduced by 438.1 grams, caused a rise in temperature of 
 3.18941 C., the difference being 0.57840 C. 
 
 Letting X = water equivalent of the bomb calorimeter, we have 
 
 2.61101 X = 3. 18941 (X- 438.1 grams) 
 X = 2,415. 77 grams. 
 
 Computed according to the first method, the water value of the 
 bomb calorimeter would be 2,415.74 grams, which is practically 
 identical with the foregoing, and 2,415.77 is considered as being the 
 correct water equivalent of this calorimeter and will be used in all 
 computations. It is, of course, the water value at 22.12 C., corre- 
 sponding to a specific heat of water of 0.99745 (compare p. 20), 
 expressed in terms of mean calories, i. e., of water at specific heat 1.0. 
 It will be seen that this agrees very closely with the value computed 
 from the weights and specific heats of the materials of the calorimeter; 
 hence the latter value used in computing the rise of temperature due 
 to the combustion of the fuse wire and of nitrogen can have intro- 
 duced no appreciable error. 
 
 CORRECTION FOR COMBUSTIBLE GASES IN TB33 OXYGEN. 
 
 Having the water value of the apparatus established, the next step 
 is to test the oxygen supply for impurities in the form of combustible 
 gases, etc. This is very important, for there is in this country at 
 the present time, at least so far as the writer knows, no perfectly 
 pure oxygen put up under high pressure for bomb-calorimeter use, 
 and hence a correction must be worked out for the oxygen used, 
 when accurate work is required. The problem may be established 
 by two different methods: 
 
 First, by noting the influence of varying pressure of oxygen upon 
 the combustibility of the gases when the same amount of heat is 
 generated in the bomb during the several combustions. 
 
 Secondly, by noting the effect of varying charges, that is, the 
 varying amounts of heat evolved, upon the combustion of the differ- 
 ent gases, the oxygen pressure in the bomb being the same.
 
 CORRECTION FOR COMBUSTIBLE GASES IN THE OXYGEN. 23 
 
 Analyzed by the copper oxid combustion method, the writer's asso- 
 ciate, Mr. Braman, found the oxygen at hand to contain 0.0161 per 
 cent of carbon and 0.0194 per cent of hydrogen by weight, and the 
 question is: Does a part, or all, of these gaseous impurities burn dur- 
 ing an energy determination, and, if burned, what will be the rise in 
 temperature caused by the burning ? 
 
 This bomb charged with 20 atmospheres of oxygen would, according 
 to the above analyses, contain 0.001648 gram of carbon and 0.001986 
 gram of hydrogen. The ratio of carbon to hydrogen is such that they 
 can not form any one gas, for even should all the carbon be present 
 as methan, there would still be 0.00144 gram of free hydrogen, which 
 alone represents about 50 calories. 
 
 It was decided to burn as large a charge of benzoic acid as would 
 possibly burn completely in 10 atmospheres of oxygen, and then burn 
 the same amount in 20 atmospheres: also to burn about half the 
 quantity of the substance in oxygen of the pressures just mentioned. 
 The final results of these tests we desire to express in terms of the 
 quantity of heat generated in the bomb and its effect upon the 
 impurities in the oxygen instead of in terms of any particular sub- 
 stance. But for our immediate purpose, we can express the rise in 
 temperature in terms of the amount of charge used, and hence in the 
 computation of the results we can make use of the newly found water 
 equivalent and follow the same method employed in finding the rise 
 in temperature per gram of substance in Table 7. 
 
 Tables 8 and 9 contain the results of two series of combustions of 
 like charges of benzoic acid burned in different amounts of oxygen 
 and the rise in temperature due to the impurities in the oxygen. In 
 the first series of combustions the charges were twice the size of those 
 in the second series. The carbon present in the form of C() 2 in the 
 bomb after a combustion was determined in some instances in the 
 case of the large charges of benzoic acid, and the average of three 
 determinations where 20 atmospheres of oxygen were used was 68.801 
 per cent of carbon, the theoretical being 68.83 per cent of carbon. 
 The three determinations with the smaller amount of oxygen gave an 
 average of 68.713 per cent of carbon, a difference of about 0.09 per 
 cent. This is an indication that the charges were a little too largo, 
 so that with 10 atmospheres of oxygen the combustions can not bo 
 relied upon as being complete. Assuming that this small difference 
 in carbon represents the actual difference between complete and 
 incomplete combustion of the benzoic acid, which can not be far 
 wrong, we have a correction which can be applied to the rise in 
 temperature obtained with 10 atmospheres of oxygen.
 
 24 
 
 METHODS AND STANDARDS IN BOMB CALORIMETEY. 
 
 TABLE 8. Rise in temperature caused by burning like quantities of benzoic add in vary- 
 ing amounts of oxygen. Results corrected for 0.032 gram water evaporation. 
 
 Oxygen 
 pressure. 
 
 Benzoic 
 acid 
 burned. 
 
 Fuse wire. 
 
 HNO 3 
 formed. 
 
 Rise in 
 tempera- 
 ture." 
 
 Rise in 
 tempera- 
 ture due to 
 wire and 
 HNO 3 . 
 
 Rise in 
 tempera- 
 ture due to 
 benzoic 
 acid. 
 
 Rise due to 
 0.7142 gram 
 benzoic 
 acid. 
 
 Atmospheres. 
 20 
 
 Gram. 
 0. 7157 
 
 Calories. 
 26.24 
 
 Calories. 
 7.10 
 
 ft 
 
 1. 8915 
 
 C. 
 0. 01380 
 
 C. 
 1. 87770 
 
 C. 
 
 1. 87377 
 
 20 
 
 .7341 
 
 22.88 
 
 7.20 
 
 1. 9371 
 
 . 01246 
 
 1.92464 
 
 1 87247 
 
 20. 
 
 .7034 
 
 26.24 
 
 6.90 
 
 1.8554 
 
 . 01372 
 
 1. 84168 
 
 1.86996 
 
 20 
 
 .7162 
 
 23.04 
 
 6.95 
 
 1.8904 
 
 . 01242 
 
 1. 87798 
 
 1.87274 
 
 20 
 
 .7110 
 
 26.56 
 
 6.95 
 
 1.8804 
 
 .01388 
 
 1.86652 
 
 1. 87492 
 
 20 
 
 .7045 
 
 23.68 
 
 6.95 
 
 1.8588 
 
 .01268 
 
 1. 84612 
 
 1.87154 
 
 
 
 
 
 
 
 
 
 Average 
 
 
 
 
 
 
 
 1. 87257 
 
 
 
 
 
 
 
 
 
 10 
 
 .7108 
 
 27.04 
 
 1.73 
 
 1. 8708 
 
 .01191 
 
 1.85889 
 
 1. 86778 
 
 10 
 
 .7134 
 
 23.36 
 
 1.73 
 
 1. 8752 
 
 . 01039 
 
 1. 86481 
 
 1.86690 
 
 10 
 
 .7112 
 
 21. 12 
 
 1.73 
 
 1. 8615 
 
 .00946 
 
 1. 85204 
 
 1.85985 
 
 
 
 
 
 
 
 
 
 Average 
 
 
 
 
 
 
 
 1.86484 
 
 
 
 
 ' 
 
 
 
 
 
 o Corrected for evaporation and for difference in water value of calorimeter due to differences in amount 
 of oxygen used. 
 
 0. 7142 gram benzoic acid in 20 atmospheres 62 1. 87257 C. rise. 
 
 . 7142 gram benzoic acid in 10 atmospheres 62 1. 86484 C. rise. 
 
 . 09 per cent incomplete combustion in 10 atmospheres O? 00168 C. rise. 
 
 Difference due to 10 atmospheres oxygen 00605 C. 
 
 TABLE 9. Rise in temperature caused by burning like quantities of benzoic acid in vary- 
 ing amounts of oxygen. Results corrected for 0.032 gram water evaporation. 
 
 
 
 
 
 Rise in 
 
 
 
 
 
 
 
 
 tempera- 
 
 
 
 
 Oxygen 
 
 pressure. 
 
 Benzoic 
 acid 
 burned. 
 
 Fuse wire. 
 
 HNO 3 
 formed. 
 
 ture cor- 
 rected for 
 evapora- 
 tion and 
 variation 
 in bomb 
 
 Rise in 
 tempera- 
 ture due to 
 wire and 
 HNO 3 . 
 
 Rise in 
 tempera- 
 ture due to 
 benzoic 
 acid. 
 
 Rise due to 
 0.3566 gram 
 benzoic 
 acid. 
 
 
 
 
 
 water 
 
 
 
 
 
 
 
 
 value. 
 
 
 
 
 A tmospheres. 
 
 Gram. 
 
 Calories. 
 
 Calories. 
 
 C. 
 
 C. 
 
 C. 
 
 "C. 
 
 20 
 
 0.3648 
 
 22.88 
 
 3.40 
 
 0.9696 
 
 0. 01088 
 
 0. 95872 
 
 0. 93717 
 
 20 
 
 .3579 
 
 21.44 
 
 3.40 
 
 .9508 
 
 . 01028 
 
 .94052 
 
 0. 93710 
 
 
 
 
 
 
 
 
 
 Average 
 
 
 
 
 
 
 
 . 93714 
 
 
 
 
 
 
 
 
 
 10 
 
 .3595 
 
 23.04 
 
 1.03 
 
 . 95245 
 
 .01000 
 
 . 94245 
 
 . 93484 
 
 10 
 
 .6301 
 
 22.88 
 
 1.03 
 
 . 95215 
 
 .00990 
 
 .94225 
 
 .93309 
 
 10 
 
 3585 
 
 25.76 
 
 1.03 
 
 . 95315 
 
 .01109 
 
 .94206 
 
 . 93707 
 
 10 
 
 .3484 
 
 26.24 
 
 1.03 
 
 . 92385 
 
 .01129 
 
 .91256 
 
 .93404 
 
 
 
 
 
 
 
 
 
 Average 
 
 
 
 
 
 
 
 . 93476 
 
 
 
 
 
 
 
 
 
 0. 3566 gram benzoic acid in 20 atmospheres O 2 0. 93714 C. rise. 
 
 . 3566 gram benzoic acid in 10 atmospheres Os 93476 C. rise. 
 
 Difference due to 10 atmospheres O s 00238 C. 
 
 Difference due to 15 atmospheres Oj 00357 C. 
 
 The smaller charges (Table 9) were completely burned in 10 atmos- 
 pheres of oxygen, which was proved by the carbon dioxid determina- 
 tion after the combustion giving 68.838 per cent of carbon. From the 
 above tables we learn that there was a greater rise in temperature 
 when the combustion took place in oxygen at high pressure than 
 when less oxygen was present. In the case of the smaller charges,
 
 COMPARISON OF RESULTS WITH BENZOIC ACID. 
 
 25 
 
 that is, less heat evolution, the difference in rise of temperature was 
 less for each atmosphere difference in pressure than in the case of 
 the greater heat. It is difficult to remove the last traces of a com- 
 bustible gas from a gas mixture by combustion or electric sparks, and 
 we can not expect that all combustible gases present in the oxygen 
 would be burned in the bomb by a single combustion of any kind 
 of substance. Further, it is to be expected that conditions may be 
 reached relative to dilution of gases, rate of combustion of the sub- 
 stance, and heat evolution when the dilute gases escape combustion 
 altogether. In the case of the 0.7142 gram of benzoic acid burned in 
 10 atmospheres oxygen pressure, the combustion of the substance was, 
 as stated, not quite complete, that is, vapors or combustible gases 
 from the burning material itself had begun to be left unburned. 
 Hence the point when the combustible gases present in the oxygen 
 supply will practically cease to be affected can not be far either way 
 from 10 atmospheres oxygen pressure, with the larger charge of 
 benzoic acid. 
 
 In order to compare the effect of the 0.3566-gram charges upon the 
 combustible gases with that of the larger ones, the resulting rises 
 in temperature are computed to the same basis and are given in 
 Table 10. 
 
 TABLE 10. Comparison of average results obtained by burning unlike quantities of 
 benzoic acid in like amounts of oxygen. 
 
 Oxygen. 
 
 Benzoic 
 acid 
 charges. 
 
 Average rise 
 in tempera- 
 ture. 
 
 Rise com- 
 puted on 
 basis of 0.7142 
 grain charge. 
 
 Atmos- 
 
 Gram. 
 
 C. 
 
 C. 
 
 pheres, 
 
 
 
 
 20 
 
 0.7142 
 
 1. 87257 
 
 1. S7257 
 
 20 
 
 .3500 
 
 .93714 
 
 1.S7691 
 
 Difference 
 
 
 
 + .00434 
 
 
 
 
 
 10 
 
 .7142 
 
 1.86484 
 
 1.86652 
 
 10 
 
 .3566 
 
 . 93476 
 
 1. 87214 
 
 Difference. 
 
 
 
 + .00562 
 
 
 
 
 
 Here we notice, first, that the smaller charges show a relatively 
 larger rise in temperature both at 10 and at 20 atmospheres; further- 
 more, the small charges, which burned completely at 10 atmospheres 
 oxygen pressure, show a greater increase over the large charges at 
 10 atmospheres than over the same when burned at 20 atmospheres 
 oxygen pressure. This is an indication that the limit for combustion 
 of the gases in the oxygen has not been reached at 10 atmospheres 
 with a small charge. With 0.3566 gram charge, therefore, we can 
 well assume that at 5 atmospheres oxygen pressure the conditions 
 for burning correspond to those at 10 atmospheres with 0.7142 gram 
 charge, i. e., twice the amount, and that, therefore, at 5 atmospheres 
 oxygen the effect upon the combustible gases would have ceased.
 
 26 METHODS AND STANDARDS IN BOMB CALORIMETRY. 
 
 Hence, the difference in rise of temperature due to combustible gases 
 present in the oxygen supply when 0.7142 gram benzoic acid is burned 
 in the bomb at 20 atmospheres can be represented by 0.0060 C. as 
 found in Table 8, and for 0.3566 gram charge at 20 atmospheres 
 oxygen 0.0036 C. (Table 9) ; for other amounts of benzoic acid burned 
 the error due to combustible gases is found by interpolation. 
 
 NATURE OF COMBUSTIBLE GASES. 
 
 As to the nature of the gas or gases which cause the rise in tem- 
 perature, we know from the CO 2 determinations that none of the 
 carbon in the oxygen was oxidized, and there remains, therefore, only 
 the free hydrogen, even a portion of which is sufficient to cause the 
 observed rise. 
 
 THE HEAT OF COMBUSTION OF BENZOIC ACID. 
 
 We now have the correct water equivalent of the calorimeter, a 
 correction for the impurities in the oxygen, and also the evaporation 
 correction, and can proceed to the computation of the heat of com- 
 bustion of benzoic acid. 
 
 In all the determinations the Regnault-Pf aundler formula, referred 
 to earlier in connection with the water value determination by means 
 of electricity, has been used for working out the radiation correction; 
 that is, the correction for the influence of the surrounding air upon 
 the readings. The computation of one of the determinations is 
 given below in detail as an example, and following that will be found 
 tabulated the results of various determinations representing a wide 
 range of conditions, both in regard to quantity of substance burned 
 and oxygen used. It is a satisfactory check upon the accuracy of 
 the bomb work when very different amounts of material are burned 
 and concordant results are obtained. 
 
 Example of a determination of heat combustion. 
 
 Substance, benzoic acid, Kahlbaum's. 
 
 Charge, 0.7157 gram. 
 
 Iron fuse wire completely burned, 0.0164 gram=26.24 calories. 
 
 Oxygen pressure, 20 atmospheres. 
 
 Room temperature, 23 C. 
 
 Water temperature before ignition, 21.26 C. 
 
 HNO 3 formed and titrated =7. 10 calories. 
 
 Ignition of charge, instantaneous. 
 
 Combustion of substance, complete. 
 
 Carbon dioxid found after combustion =68. 801 per cent carbon. 
 
 Thermometer readings, preliminary 1.438; 1.440; 1.442; 1.444; 1.445. 
 
 Thermometer readings, corrected 1.4468; 1.4538. 
 
 Combustion period readings 1.445; 2.920; 3.292; 3.316; 3.317. 
 
 Combustion period readings, corrected .. 1.4538; 2.9343; 3.3058; 3.3297; 3.3307. 
 
 Thermometer readings, end period 3.317; 3.313; 3.311; 3.309; 3.308. 
 
 Thermometer readings, end period, corrected .. 3.3307; 3.3208.
 
 THE HEAT OF COMBUSTION OF BENZOIC ACID. 
 
 27 
 
 r=0.0018 
 f= 1.4503 
 0=5 
 
 v= -0.0025 C. 
 
 t= 3.3258 C. 
 
 Thermometer lag= -0.0005 C. 
 
 IAt= +0.0073 C. 
 
 Last reading of combustion period 
 
 First reading of combustion period 
 
 Radiation correction 
 
 Correction for thermometer lag 
 
 Correction for impurities in oxygen 
 
 Evaporation of water during 4 minutes 
 
 Corrected rise in temperature 
 
 Water value of bomb system with 20 atmospheres oxygen 
 (2415.8) X1.8855 C ...................................... 
 
 Correction for fuse wire ..................................... 
 
 Correction for HNO 3 ........................................ 
 
 C. 
 
 +3. 3307 
 -1.4538 
 + .0073 
 
 - .0005 
 
 - .0060 
 + .0078 
 
 1. 8855 
 Calories. 
 
 4, 554. 99 
 -26. 24 
 - 7.10 
 
 4, 521. 65 
 4521.65-5-0.7157=6317.80 calories per gram benzoic acid. 
 
 In like manner all the results found in the following table are worked 
 out: 
 
 TABLE 11. Heat generated when different quantities of benzoic acid are burned in varying 
 amounts of oxygen, and the heat of combustion per gram of benzoic acid. 
 
 Oxygen 
 pressure. 
 
 Henzoic 
 acid, 
 burned. 
 
 Fuse 
 wire. 
 
 HN0 3 
 formed. 
 
 Observed 
 rise in 
 tempera- 
 ture. 
 
 Corrected 
 rise in 
 tempera- 
 ture. 
 
 Total heat 
 generated 
 in the 
 bomb. 
 
 Heat per 
 gram ben- 
 zoic acid. 
 
 Tempera- 
 ture of 
 water be- 
 fore igni- 
 tion. 
 
 Atmos- 
 
 
 
 
 
 
 
 
 
 pheres. 
 
 Gram. 
 
 Calories. 
 
 Calories. 
 
 C. 
 
 O ft 
 
 Calories. 
 
 Calorics. 
 
 C. 
 
 25 
 
 0.7088 
 
 23.36 
 
 8.25 
 
 1.8635 
 
 1.8655 
 
 4, 506. 75 
 
 6,313.68 
 
 21.3 
 
 20 
 
 .7157 
 
 26. 24 
 
 7.10 
 
 1.8769 
 
 .8855 
 
 4, 554. 99 
 
 6,317.67 
 
 21.3 
 
 20 
 
 .7341 
 
 22.88 
 
 7.20 
 
 1.9288 
 
 .9311 
 
 4,665. 15 
 
 6.313.96 
 
 20.8 
 
 20 
 
 . 7084 
 
 26. 24 
 
 6.90 
 
 1.8408 
 
 .8494 
 
 4, 467. 79 
 
 6. 304. 73 
 
 20.7 
 
 20 
 
 .7162 
 
 23.04 
 
 6.95 
 
 1.8804 
 
 .8844 
 
 4,552.34 
 
 6.314.37 
 
 21.4 
 
 20 
 
 .7110 
 
 26. 56 
 
 6.95 
 
 1.8653 
 
 .8744 
 
 4,528.18 
 
 6,321.62 
 
 20.9 
 
 20 
 
 .7045 
 
 23. 68 
 
 6.95 
 
 1.8435 
 
 .8528 
 
 4. 476. 00 
 
 6,309.97 
 
 21.3 
 
 15 
 
 .7100 
 
 26.24 
 
 4.40 
 
 1.8448 
 
 1. 86735 
 
 4.511.15 
 
 6. 3 10. ,58 
 
 20.4 
 
 20 
 
 .3648 
 
 22.88 
 
 3.40 
 
 .9591 
 
 .9660 
 
 2, .333. 67 
 
 6, 325. 07 
 
 20.4 
 
 20 
 
 .3579 
 
 21.44 
 
 3.40 
 
 .9411 
 
 .9472 
 
 2,288.25 
 
 6, 324. 13 
 
 20. 3 
 
 10 
 
 .3595 
 
 23.04 
 
 1.03 
 
 .9431 
 
 .95125 
 
 2. 298. 03 
 
 6, 325. 33 
 
 19.8 
 
 10 
 
 .3001 
 
 22.88 
 
 1.08 
 
 .9427 
 
 .95095 
 
 2.297.31 
 
 6.313.24 
 
 19.9 
 
 10 
 
 .3585 
 
 25. 76 
 
 1.03 
 
 .9390 
 
 .95195 
 
 2, 299. 73 
 
 6, 340. 13 
 
 20.5 
 
 10 
 
 .3484 
 
 26. 24 
 
 1.03 
 
 . .9095 
 
 . 92265 
 
 2. 228. 95 
 
 6.319.38 
 
 20.7 
 
 Average 
 
 
 
 
 
 
 
 6,318. 12 
 
 20.7 
 
 
 
 
 
 
 
 
 
 
 In the above table representing fourteen determinations made 
 under such varied conditions the results agree very well; for if we 
 leave out the two extreme results the greatest difference from the aver- 
 age in the remaining twelve determinations is but 8.15 calories. Com- 
 puted by the usual formula, the probable error of the mean of the
 
 28 METHODS AND STANDARDS IN BOMB CALOKIMETRY. 
 
 fourteen determinations is 1.51 calories and the probable error of 
 a single determination 5.69 calories. 
 
 SULPHUR, PHOSPHORUS, AND CHLORIN. 
 
 The writer sometime ago called attention to the fact that the 
 acid found in the bomb after a combustion is not always HNO 3 alone, 
 and that it is especially the S in organic combination, which goes over 
 into gaseous SO 3 and eventually into H 2 SO 4 , that needs to be con- 
 sidered. Hence the sulphuric, phosphoric, and hydrochloric acids 
 are determined when found in sufficient quantities, and the total 
 acidity found by titration is correspondingly corrected in computing 
 the heat arising from the oxidation of free nitrogen. Determinations 
 of sulphur and phosphorus have been successfully carried on in feeds, 
 feces, and urines by the bomb method during these last three years 
 in this laboratory. In the two samples of benzoic acid which were 
 used in the above determinations, one, Kahlbaum's best, gave no 
 test for Cl. and only a light trace of SO 3 . The other sample, " Merck," 
 gave but a small trace of SO 3 and a distinct trace of CL, but in no 
 case enough to be determined for the sake of correction. 
 
 CORRECTION FOR THE SPECIFIC HEAT OF WATER. 
 
 Since the specific heat of water differs at different temperatures, 
 the water equivalent of the calorimeter will also vary with the tem- 
 perature. In the above case the water equivalent was determined 
 with an average of 21.08 C. water temperature before the combus- 
 tions and an average of 23.15 after the combustions. The mean 
 specific heat between these temperatures is 0.99745. The mean 
 specific heat between the average temperatures before and after 
 combustions in the fourteen determinations of Table 11 is 0.99752. 
 
 The true average heat of combustion, therefore, is 
 
 6,318.12 X; = 6,318.56 calories. 6 
 99745 
 
 CHANGE IN THE BOMB CONTENTS. 
 
 There are at least two other conditions which should be consid- 
 ered, since they may to some small degree influence the heat of com- 
 bustion as computed from the determinations already described and 
 recorded in Table 1 1 . 
 
 One is a possible change in the water value of the calorimeter 
 which may be caused by the combustion of the substance in the 
 bomb. According to the nature of the substance, the contents of 
 
 a U. S. Department of Agriculture, Bureau of Animal Industry Bulletin 94, p. 32. 
 
 b This method of computation assumes, of course, that the specific heats of the 
 materials of the calorimeter itself vary with the temperature at the same rate as does 
 that of water. The total correction is so small, however, that any error thus intro- 
 duced must be insignificant.
 
 CHANGE IN THE BOMB CONTENTS. 29 
 
 the bomb will change more or less, so as to make the water equiva- 
 lent after the combustion different from what it was before. 
 
 When the same kind of material is burned as that which was used 
 for the determination of the water value of the bomb, the changes 
 need not be considered except when a different quantity is burned. 
 Should an entirely different compound be burned, even if in a quan- 
 tity like that used for water value determinations, the condition 
 existing in the bomb before and after combustion should be com- 
 puted whenever it is possible to do so, in order to determine whether 
 enough change took place in the water equivalent of the bomb to 
 call for a correction. In the computations we use the following values : 
 
 Volume of gas in bomb at 20 atmospheres, measured at 20 C., 
 730 mm. pressure, is 8 liters. 
 
 Grams. 
 
 Weight per liter O 2 at 20, 730 mm 1. 2798 
 
 Specific heat (X, constant volume 157 
 
 Specific heat, CO.,, constant volume 149 
 
 Specific heat benzoic acid, computed 30 
 
 Specific heat Fe 3 O 4 167 
 
 Specific heat Fe 2 1114 
 
 Specific heat HNO 3 445 
 
 Specific heat H 2 1. 0000 
 
 The average of 10 charges used in the water value determinations 
 equals 0.7102 gram benzoic acid, and considering all the gas as oxygen 
 we have in the bomb before the combustion the following water 
 equivalent : 
 
 Grams HjO. 
 
 Benzoic acid, 0.7102 gram X0.30 0. 2131 
 
 Oxygen, 8X1.2798X0.157 1. 6074 
 
 Iron wire, 0.0164 X0.1114 0018 
 
 Total 1. 8223 
 
 After the combustion there are in the bomb the following substances: 
 
 Grams. 
 
 Carbon dioxid, 0.7102X2.5246 1. 7930 
 
 Water, 0.7102X0.4426 3143 
 
 FeaO,, 0.0164X1.381 0227 
 
 Oxygen, 10.2384-1.4309 8. 8075 
 
 N 2 O 5 0275 
 
 This is equivalent to the following amounts of II,O: 
 
 Grams lljO. 
 
 1.7930 grams C0 2 X0.149 0. 2(572 
 
 .3143 gram H,OX 1.000 3143 
 
 .0227 gram Fe 3 O 4 X0.167 0039 
 
 .0321 gram HXO 3 X0.445 -0.0046 0097 
 
 8.8075 grams O 2 X0.157 1. 3S28 
 
 Total 1. 9779 
 
 Thus with benzoic acid there is a change of only about 0.10 gram 
 water equivalent caused by the combustion. 
 
 "Average for this locality.
 
 30 METHODS AND STANDARDS IN BOMB CALORIMETBY. 
 
 If instead of benzoic acid, 0.7 gram of ethyl alcohol were burned, 
 we should find a difference of about 0.39 gram water equivalent 
 caused by the combustion and about 0.44 gram water equivalent 
 different from that obtained by benzoic acid. The average charge 
 hi the fourteen determinations of Table 11 equals 0.5609 gram, and 
 the average charge used in standardizing the bomb was 0.7102 gram, 
 which is equivalent to a difference of 0.08 gram in the water value of 
 the bomb, or a correction of 0.20 calorie per gram in the average 
 result. This is a very small correction and usually need not be 
 considered at all. 
 
 CHANGE OF PRESSURE IN THE BOMB. 
 
 The second condition referred to above is the change in pressure 
 in the bomb resulting from the combustion. By the heat of com- 
 bustion of a substance is generally understood the heat at constant 
 pressure, which is in many instances slightly different from that 
 determined by the bomb calorimeter at constant volume. Since it 
 is the difference between the conditions before and after the combus- 
 tion which is considered, it makes no difference what pressure the 
 gases may be under in the bomb before the combustion. If the 
 pressure of the gases before and after the combustion remains the 
 same, the heat of combustion at constant volume and constant pres- 
 sure is the same. Leaving out of account the small changes due to 
 the oxidation of iron and the formation of nitric acid in the bomb, 
 this is theoretically true of carbohydrates where CO 2 and O 2 replace 
 each other volume for volume. With other substances it may be 
 different. At constant pressure compounds containing much hydro- 
 gen will cause a decrease in volume of the gases and hence require a 
 plus correction, and compounds with less hydrogen but plenty of nitro- 
 gen may cause an increase in gas volume, and consequently there will 
 be a minus correction to the results obtained by the bomb. 
 
 For a solid or liquid substance of the composition C n H p O q burned 
 at constant volume in the bomb the heat at constant pressure is 
 expressed by the following formula : 
 
 = CtV+0.5424 g-+ 0.002 r 
 
 where 
 
 t = temperature. 
 
 p and q = number of atoms in the molecule. 
 
 According to this formula, benzoic acid, C 7 H 6 O 2 , at constant pres- 
 sure will be : 
 
 (HP = Ct V+ 0.5424 X^ + 0.002X^-^X22.8 
 
 which expressed in calories per gram equals: 
 
 6,318.56 + 2.41 =6,320.97 per gram benzoic acid. 
 
 Beila^e zum Ohemiker-Kalemler, 1904, p. 144.
 
 USE OF BOMB CALORIMETER UNDER DIFFERENT CONDITIONS. 31 
 
 If to this we apply the correction found for the change in the bomb 
 content bepause of unlike charges, 0.20 calorie, the heat of combus- 
 tion of 1 gram benzoic acid, C 7 H 6 O 2 , at constant pressure will be: 
 6, 320. 77 1.51 mean calories, a value practically identical with that 
 found by Stohman, viz, 6,322 calories. 
 
 USE OF THE BOMB CALORIMETER UNDER DIFFERENT CON- 
 DITIONS. 
 
 Judging from these investigations, there are many conditions 
 which may influence the work with the bomb and cause the results 
 to become inaccurate, and the question is, What is the best and most 
 convenient way to operate the bomb so as to get reliable results 
 under the various conditions? Three methods in regard to the 
 determination of the water value of the calorimeter and its use may 
 be employed according to existing laboratory and other conditions: 
 
 1. The apparent water value may be directly determined by 
 burning a given weight of a standard substance, note being taken 
 of all the conditions existing at the time of standardization of the 
 bomb, including amount of substance and of oxygen, and atmospheric 
 conditions influencing evaporation. If, now, the substance to be 
 analyzed corresponds in quantity to the calories generated at the 
 standardization, and if the other conditions are the same, there will 
 be no corrections to apply for impurity in oxygen or for evaporation 
 of water. Whether the small correction for constant volume and 
 for change in contents of the bomb need to be applied depends upon 
 the degree of accuracy to which the operator expects to work. 
 
 2. Should it be required to burn charges giving much more or less 
 heat than that used for standardization, with the oxygen supply and 
 evaporation condition remaining unchanged, then it is most con- 
 venient to have the water value of the bomb determined with the 
 smaller or larger charges also, and thus avoid the use of corrections. 
 
 3. When, however, the heat determinations must be made under 
 varying temperature conditions, with different amounts of substance 
 and various oxygen supplies, then all the corrections due to variation 
 from the conditions at which the bomb was standardized must be 
 applied. 
 
 The different water values for the bomb calorimeter used in this 
 work corresponding to the above three methods of usage would be, 
 including 2,000 grams of water; 
 
 Method 1, with 0.7142 gram benzoie acid charge, 2.421 water 
 value. 
 
 Method 2, with 0.3614 gram benzoic acid charge. 2,425.4 water 
 value. 
 
 Method 3, with 0.7102 gram benzoic acid charge, 2,415.7 water 
 value. 
 
 In the third or last value, the corrections due to evaporation of 
 water and specific heat of water have been applied.
 
 32 
 
 METHODS AND STANDARDS IN BOMB CALORIMETRY. 
 
 CORRECTIONS FOR IMPURITIES IN OXYGEN. 
 
 Having now the specific heat of combustion of benzoic acid, we 
 can find from Tables 8 and 9 the correction for impurities in the 
 oxygen expressed in degrees rise of temperature, or its equivalent 
 in calories, for any given amount of heat generated in the bomb 
 during a combustion. All substances do not affect the combustible 
 gases alike, but for this purpose we may assume benzoic acid to be a 
 representative substance, and each kind of material need not be 
 tested separately. The average of six charges of benzoic acid was 
 0.7142 gram, which, multiplied by 6,320.8 equals 4,514.3 calories. 
 This amount of heat caused a rise in temperature of 1.87257 C. with 
 20 atmospheres oxygen, and with 10 atmospheres oxygen a rise of 
 1.86652 C., a difference of 0.00605 C., which is equal to 14.62 
 calories. In like manner, the average charge, 0.3566 grams benzoic 
 acid, Table 9, equals 2,254 calories and causes a total difference of 
 0.00357 C. rise, equivalent to 8.59 calories. 
 
 By interpolation we have, according to the various amounts of heat 
 generated in 20 atmospheres oxygen pressure, the corrections for the 
 oxygen shown in Table 12. They are applicable, of course, only to the 
 particular sample of oxygen used in these determinations, and unless a 
 uniform quality of the oxygen in this respect can be assured, it would 
 be necessary to redetermine their factors for each cylinder of oxygen. 
 
 TABLE 12. Corrections for combustible gases in oxygen. 
 
 Heat gene- 
 rated in 
 bomb. 
 
 Correction in terms of 
 
 Rise of tem- 
 perature. 
 
 Calories. 
 
 Calories. 
 4,500 
 4,000 
 3,500 
 3,000 
 2,500 
 2,250 
 2,000 
 
 C. 
 0.00603 
 0.00550 
 0.00495 
 0.00440 
 0.00385 
 0.00357 
 0. 00330 
 
 14.55 
 13.22 
 11.89 
 10.57 
 9.24 
 8.58 
 7.91 
 
 BENZOIC ACID AS A STANDARD. 
 
 From his experience with various substances, and because of the 
 value obtained for benzoic acid as described in this paper, the author 
 in conclusion urges all persons using the bomb calorimeter for scien- 
 tific work where results are to be published, for the sake of uniformity 
 and comparability of results, to adopt benzoic acid as the one single 
 standard against which to standardize the bomb, and to accept 6,322 
 calories per gram as its heat of combustion. This is the value accred- 
 ited to Stohhmann, and this value ought to remain the standard until 
 it has been definitely proved to be erroneous and a new value in some 
 way officially recognized or accepted. 
 
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