988 REPORT—1885. 
Atoms,’ Nature, March 31, 1870) have led up to the conclusion that the number 
of molecules in each cubic millimetre of a gas at atmospheric temperatures and 
pressures is somewhere about a unit-eighteen (10'%). Hence, the number of 
molecules in a litre will be about a unit-twenty-four (104). Now, a litre of hy- 
drogen at atmospheric pressures and temperatures weighs, roughly speaking, a 
decigramme There isno advantage in taking account of the ratio of 1-2 decigramme 
to 1 decigramme. Hence, the mass of .a molecule of hydrogen, or weight, as it 
is called by chemists, is a quantity of the same order as a decigramme divided by 
10**—1.e. a twenty-fourth decigramme, which is the same as the twenty-fifth 
grammet. (The grammets are the decimal subdivisions of the gramme, of which 
the first is the decigramme, the second the centigramme, and so on.) Hence, the 
mass of the chemical atom of hydrogen may be taken to be about half the twenty- 
fifth of the grammets. There is no use in retaining the co-efficient ‘half’ in an 
estimate in which we cannot be certain to a unit that we have assigned the right 
power of 10, and we may, therefore, for the sake of simplicity, take the twenty- 
fifth grammet itself as being such an approach as we can attempt to the value of 
the mass of the chemical atom of hydrogen. 
Having obtained the mass of one atom, that of hydrogen, the masses of the 
atoms of the other simple substances bear the ratios to this that are assigned to 
them in the table of atomic weights, and the masses of molecules of compounds 
can be derived directly from these in accordance with their formulz, so that ail 
are approximately known. 
7. On Macromolecules (Molecules of Matter in the Crystalline State as 
distinct from the Chemical Molecule), and determinations of some of 
them. By G. JouNstone Sronty, D.Sc, F.R.S. 
The molecule of a crystal is usually found, in the few cases in which an inves- 
tigation is possible, to include several chemical molecules. On this account the 
author has suggested that they be called macromolecules, as in reference to them 
the chemical molecule is a sub-molecule. 
In a communication made two years ago to the British Association, it was shown 
that although each chemical atom of a solid may be in a state of internal motion, 
this motion must be such that a point can be assigned within each atom (and which is 
determined by an integration similar to that by which centres of gravity are deter- 
mined) which point is a fixed point in solids, and a travelling point if the atom be 
an atom of a liquid or gas. This for convenience may be called the centre of the 
atom. Ina crystal, these centres are all in fixed positions and at definite distances 
asunder, so that a diagram may be conceived consisting of these points, with lines 
connecting them wherever the corresponding atoms are chemically in combination. 
The chemical formula limits geometrically the number of positions relatively to 
one another in which these points can stand within one chemical molecule. 
The only hypothesis that needs to be made is at this stage and the next, at 
both of which it is assumed that the bonds or connections between the chemical 
molecules of a solid are identical with the bonds found by Chemistry between the 
atoms of chemical molecules, being some not used in forming that particular sub- 
molecule. 
By this hypothesis the diagram can be extended to a group of chemical 
molecules, and, as before, there is geometrically only a limited number of such 
diagrams possible. 
Finally, these groups or macromolecules are again connected together by 
chemical bonds not yet employed, and these final connections must be such that 
the resulting form &c. are identical with the observed crystalline form with all its 
faces and with its cleavage planes, &c. All these when known furnish conditions 
that limit the number of possible arrangements at the preceding stages, and if the 
number of such conditions be sufficient, or where the crystalline form is sufficiently 
complicated, and especially where hemihedral faces occur, they give an indication 
as to which of the possible arrangements at the preceding stages is the real one. 
In a few cases it has been possible in this way to make out with considerable 
