=

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 x 2 = 7074, which is very nearly equal to the molecular weight calculated from Regnault's numbers, hence 70-74 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 16'1 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 x 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.

Hg2+ Cl = 2 HgCl,
Volumes 4+ 4 = 4

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 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

III

V

II
Sp. gr.
as gas

IV
Molecular

weight

Name of compound

Sp. gr.

Analysis, stated in parts per molecule, hydrogen being taken as unity

X 28 87

20'0

1 Hydrofluoric acid

0 693

201 19ʻi fluorine

+ 1 hydrogen Hydrochloric acid

I'247 36'o 36 37 35-37 chlorine +1 Hydrobromic acid 2971 78.23 8075

79975 bromine

+I
Hydriodic acid

4'443

1280 127:53 126-53 iodine +1 Water

0:623 17.99

17-96

15'96 oxygen +2
Sulphydric acid

I'191 34'4 3398 3198 sulphur +2
Sulphurous oxide
2'247 649 63'90

31*98

+31'92 oxygen
Sulphuric oxide

3'01
86:09
79-86

+ 47.88 Sulphuryl chloride 4:67 134:8 13464 3198

+31'92

+70°74 chlorine 2 Selenion hydride

2795 80*54 80:8 78.8 selenion +2 hydrogen Selenious oxide

4'03 1160 1109 78.8

+31.92 oxygen 3 Tellurium hydride

4:49 129662 1295

127-5 tellurium

+2 hydrogen Ammonia

0-597 17'2 17'01 14'01 nitrogen Nitric oxide 1'039 30'0 29'97 I4OI

+15'96 oxygen Nitrogen dioxide

1'50
43:3 45'93 14'01

+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.

31'98

+3

I

II Sp. gr. as gas

III IV

V

Name of compound

Sp. gr.
X 28-87

Molecular weight

Analysis, stated in parts per molecule, hydrogen being taken as unity

2:31
1'15
2:19

4.88

14:46
5:40

5.88
4.60

Nitrosyl chloride
Phosphorous trihydride
Phosphoric fluoride
Phosphorous chloride
Phosphorous iodide
Phosphoryl chloride
Thiophosphoryl chloride
Triethyl-phosphine oxide
Arsenic trihydride
Arsenious chloride
Cacodyl chloride
Cacodyl cyanide
Methyl arsenite
Arsenious iodide
Antimonious chloride
Antimonious ethide
Bismuthous chloride
Boron trifluoride
Boron trichloride
Boron tribromide
Boron trimethide
Methane
Methyl fluoride
Methyl chloride
Methyl bromide
Methyl iodide
Chloroforin

2695
6'30
4'56
4:63
6.006
16:1

66.68
33'1
63.23
140*9
4171
155'9
16997
1328

77:8
1819
1317
1337
1734
46408
2247
2148
32797

66.8
113:8
1160S
25395
55'7
16'o
34'3
50'1
939
1410
1213

65-34
33'96
126 46
137'07
410955
15303
169'05
13374

77.90
1810
J40'2
130:8
1697
454'5
226:1
206.8
314'1

68-3
1170
250*2
55'9
15'97
34:10
50*34
94972
14150
119'08

14oj nitrogen +15'96 oxygen +35:37 chlorine 30'96 phosphorus +3 hydrogen 30'96

+95-5 fluorine 30*96

+106-11 chlorine 30*96

+379-59 iodine
30°96

+ 106'11 chlorine +15'96 oxygen
30'96
+ 106'11

+31°98 sulphur
30'96

+15'96 oxygen +71.82 carbon +15 hydrogen
74'90 arsenic +3 hydrogen
74'90

+ 106'11 chlorine
749

+ 35-37 chlorine +23'94 carbon +6 hydrogen
74:9

+ 14'on nitrogen +35'91 carbon +6 hydrogen 74'9

+47:88 oxygen +35'91 carbon +9 hydrogen 749

+379-59 iodine
120 antimony + 106'11 chlorine

+7182 carbon +15 hydrogen
208 bismuth + 106'll chlorine

+57-3 fluorine
10'95

+ 106'11 chlorine 10'95

+239-25 bromine 10'95

+35'91 carbon +9 hydrogen II 97 carbon

+4 hydrogen 1197

+ 19'1 fluorine +3 hydrogen II97

+3537 chlorine +3 11'97

+79975 bromine +3 11'97

+126 53 iodine +3 II'97

+106'11 chlorine + 1 hydrogen

7.8

I20

10-95 boron

7:44
11'35
2'312

3942
14'02

8.78
1'93
0'555
I'186
1'736
3'253
4:883
4'20
IT'97 carbon
II'97
1197
11'97
II'97
11'97
11'97
11'97
11'97
11'97
11'97
28 silicon
28
28
28
28
48 titanium
90 zirconium
17:8 tin
117.8
117.8
117.8
117.8
117.8
117.8
203*64 thallim
206-4 lead

+141.48 chlorine
+15'96 oxygen
+3192
+15'96 +70*74 chlorine
+15'96 +31'98 sulphur
+63'96 sulphur
+ 14'or nitrogen + i hydrogen
+14'01

+3537 chlorine
+14'01

+15'96 oxygen + i hydrogen
+15'96 oxygen +4 hydrogen
+14'or nitrogen+ 3 hydrogen +47:88 oxygen
+76*4 fluorine
+141'48 chlorine
+ 506'12 iodine
+95-76 carbon + 20 hydrogen
+ 106-11 chlorine+ i hydrogen
+141.48
+14148
+14148
+319 bromine
+70-74 chlorine
+95-76 carbon +20 hydrogen
+35-37 chlorine +71.82 carbon +15 hydrogen
+79975 bromine +71.82

+15
+126-53 iodine +35'91 +9
+35-37 chlorine
+47-88 carbon +12 hydrogen
+70-74 chlorine
+70-74
+23-94 carbon +6 hydrogen
+47.88 +10
+159'5 bromine

112 cadmium

B