pound in the state of gas. Thus Regnault found for the specific gravity of chlorine the number 2'44, which multiplied into 28.87 gives 70'44. The combining weight of chlorine as most carefully determined by Stas is 35'37: now 35°37 × 2 =7074, which is very nearly equal to the molecular weight calculated from Regnault's numbers, hence 7074 is taken to be the molecular weight of chlorine. Again, Thomson found the specific gravity of marsh gas to be 0'557, which multiplied into 28.87 gives 161 as approximately the molecular weight of this compound: the combining weight of carbon is 2.99 (H = 1), and in marsh gas carbon and hydrogen are united in the proportion of 2'99 to 1, hence the molecular weight of this gas is 3'99 or a multiple thereof. But 3'99 × 4= 15'96, therefore the molecular weight of marsh gas is taken to be 15.96. The numbers in column v of the table on p. 31 represent the molecular weights of the various elements found by the method of specific gravity aided by determinations of the combining weights of the elements in question. 18. Facts have already been mentioned which on the assumption of the truth of Avogadro's law oblige us to conclude that in certain chemical reactions the molecules of the reacting elementary bodies undergo subdivision; indeed we are forced to the conclusion that the greater number of the elementary molecules are not homogeneous but are built up of smaller parts'. Now it is evident that the molecule of an element cannot contain less than two of these smaller parts or atoms, unless indeed the atom and molecule should be identical; and that the molecule of a compound cannot contain less than one atom of each of its constituent elements. Therefore if we determine the smallest amount by weight of an element in the molecule of any compound thereof, we shall have determined the maximum atomic weight of the element in question. Hence we arrive at the following definition. 1 Reactions are known in which it is not necessary to assume that subdivision of elementary molecules occurs, e.g. The maximum atomic weight of an element is the smallest quantity, in terms of hydrogen as unity, of that element in the molecule of any compound thereof. Molecular weight has been already defined as weight of two volumes of any gas referred to the weight of two volumes of hydrogen; hence the data which must be obtained before the maximum atomic weight of an element can be determined are, (1) specific gravity of a series of gaseous compounds of the element in question, and (2) careful analyses of these compounds. Suppose it is required to determine the maximum atomic weight of oxygen, such data as are indicated in the following table are obtained. Data for determining maximum atomic weight of oxygen. If the smallest weight of hydrogen found in a molecule of any compound of that element is called one, then in no molecule of any of the compounds in this table is there less than 15.96 parts by weight of oxygen; this number is therefore adopted as the maximum atomic weight of oxygen. 19. The following table (taken for the most part from Lothar Meyer's Die modernen Theorien der Chemie) contains the most important data hitherto accumulated for determining the maximum atomic weights of the elements by the application of Avogadro's law. Data for determining maximum atomic weights*. Note. The numbers expressing specific gravities of the gaseous compounds have been determined at various temperatures; the range of temperature has been sufficient to obviate errors due to changes of specific gravity accompanying changes of temperature [see ante, p. 33]; in many cases the number given is the mean of several estimations. The numbers in column IV headed Molecular weight' are obtained by the method of specific gravities aided by determinations of the combining weights of the various elements, as explained on pp. 34—35. I V Analysis, stated in parts per molecule, hydrogen being taken as unity II III Sp. gr. X 28 87 IV +47.88 Sulphuryl chloride 4.67 +31.92 2 Selenion hydride 2'795 80*54 80.8 78.8 selenion Selenious oxide 3 Tellurium hydride 4'49 129.62 129'5 Ammonia 0'597 17.2 17 ΟΙ 1275 tellurium 14'01 nitrogen + 2 hydrogen +31'92 oxygen +2 hydrogen +3 Nitric oxide Nitrogen dioxide +15'96 oxygen +3192 "" * It has not been considered necessary to give references to all the papers where full accounts of determinations of the specific gravities of the compounds in this table are to be found; most of the numbers have been for years considered as among the well established data of the science. Notes are appended giving references, &c. in all cases of especial interest, or where explanation of the numbers appears to be called for. 14'01 nitrogen V Analysis, stated in parts per molecule, hydrogen being taken as unity +15.96 oxygen +35'37 chlorine Phosphorous trihydride 115 33'1 33'96 3096 phosphorus +3 hydrogen Phosphoric fluoride 2'19 63.23 126.46 +95'5 fluorine Phosphorous chloride 4.88 140'9 137'07 30.96 +10611 chlorine Phosphorous iodide Phosphoryl chloride Thiophosphoryl chloride 5.88 Triethyl-phosphine oxide 4'60 Arsenic trihydride 2.695 77.8 77'90 74'90 arsenic Arsenious chloride Cacodyl chloride Cacodyl cyanide Methyl arsenite Arsenious iodide 16.1 Antimonious chloride 7.8 224'7 226'I 120 antimony +106 11 chlorine +35°37 chlorine+23'94 carbon +6 hydrogen +1401 nitrogen +35'91 carbon +6 hydrogen +47.88 oxygen +35 91 carbon +9 hydrogen +379'59 iodine Boron tribromide 8.78 253'5 250'2 10'95 +239 25 bromine +35'91 carbon + 9 hydrogen + 4 hydrogen +191 fluorine +3 hydrogen +35 37 chlorine +3 +79'75 bromine +3 +126 53 iodine +3 Chloroform 4'20 1213 119'08 11'97 +106 11 chlorine + 1 hydrogen +15'96 oxygen +4 hydrogen +1401 nitrogen + 3 hydrogen + 47.88 oxygen +764 fluorine +14148 chlorine +506'12 iodine +95.76 carbon +20 hydrogen +10611 chlorine+1 hydrogen Titanic chloride 6.84 197'5 189'5 48 titanium Zirconium chloride 8.15 235'4 231'5 90 zirconium Stannic chloride 9'20 265'7 259'3 II78 tin Stannic bromide 7'9 458'0 436.8 +319 bromine 4 Stannous chloride 6:45 186.2 188.5 Stannic ethide 8:02 231.6 233.6 Stannic triethyl chloride 8.43 243'4 240'0 117.8 " Stannic triethyl bromide 9'92 286.4 Stannic triethyl iodide Thallous chloride 8.22 237'4 239'0 20364 thallim Lead tetramethide Lead dichloride 9.6 277'2 266.3 206'4 lead 9'5 274'2 277'2 Zinc chloride 4.6 132.8 135.6 Zinc methide 3.29 95'0 94.8 Zinc ethide 4.62 123'0 122.8 Cadmium bromide 9'25 267'0 271'5 112 cadmium +70'74 chlorine +95.76 carbon +20 hydrogen +35 37 chlorine +71.82 carbon + 15 hydrogen +126'53 iodine +35'91 +35 37 chlorine +47.88 carbon + 12 hydrogen +70'74 chlorine +23'94 carbon +6 hydrogen +159'5 bromine |