984 REPORT— 1885. 
After having argued the probability of the theory from first principles, the 
author traces several systems of symmetrical arrangement for various different 
atom proportions, and points out that these systems are in harmony with the 
known crystal forms. The pair of systems which he derives for the atom propor- 
tions of quartz have spiral dispositions of the same kind of atom, right-handed 
in one, left-handed in the other, such as may account for the production of right- 
handed or left-handed rotation of a polarised ray by crystals of the substance. 
The cause of dimorphism is suggested, and symmetrical systems of arrange- 
ment of the atoms indicated for the dimorphic forms cale-spar and aragonite. 
The different expansion in different directions of crystals not of the regular 
system is explained. 
The phenomenon of twin crystals is shown to be in harmony with the theory. 
A general theory of isomorphism is submitted; the case of isomorphism of 
ammonic sulphate and potassic sulphate being specially referred to. 
8. On the use of Sodium or other soluble Aluminates for softening and 
purifying hard and impure water, and deodorising and precipitating 
sewage, waste water from factories, &c. By F. Maxwett Lyre, F.C.S. 
Roscoe gives the formula for sodium aluminate as Na,Al,O,, and this nearly 
agrees with the composition of the soluble portion of the crude salt. But, owing 
to its tendency to lose alumina on keeping in solution, even in closed bottles, and 
to the invariable presence of soluble silicates, the dissolved salt has practically 
rather the formula Na,A1,0,. 
Sodium aluminate is decomposed by all soluble acids and acid salts, and even 
by many strictly so-called neutral salts, among them being the sulphates, chlorides, 
and nitrates of the earthy and heavy metals. In this latter case a corresponding 
portion of earthy or metallic hydroxide is liberated, or rather the earthy or metallic 
oxide remains so loosely combined with the precipitated alumina that it is prac- 
tically free even to the point of being decomposed by carbonic acid, with the forma- 
tion of a carbonate of the base it contains, thus destroying a like amount of tem- 
porary hardness if present, just as the aluminate itself has already destroyed a 
certain number of degrees of permanent hardness. Thus (if we adopt Roscoe’s 
formula)— 
Na,A1,0, + CaSO, + CO, + 3H,0 = 
Na,SO, + 1CaCO, + Al,(HO),. 
The aluminium hydroxide takes down several times its own weight of organic 
matter, and thus may be produced— 
(A) Precipitation of any organic impurity. 
(B) Destruction of the permanent hardness, 
(c) Destruction of the whole or part of the temporary hardness. 
If the permanent and temporary hardness balance one another—z.e., are equal 
in amount—an addition of aluminate only sufficient for the permanent hardness 
will gradually destroy both it and a like number of degrees of temporary hardness. 
But if, as however is not often the case, the permanent hardness so far exceeds 
the temporary that there is not sufficient carbonic acid in solution to throw down 
as carbonate all the lime or other base producing the permanent hardness, a little 
sodium bicarbonate may be added, or, in order to keep down to a minimum the 
soluble sodic salts, a little phosphoric acid. 
If the temporary hardness be in excess, it may be destroyed by Clark’s method, 
or a little more aluminate may be added. 
The time required for the precipitation of the aluminium salts and formation of 
the calcium and other carbonates, varies with different waters from a few minutes to 
a few hours, so that where time is an object it may be advisable to use some kind 
of rough filter. Indeed water so softened and purified passes easily and filters 
perfectly. Where water is contaminated with organic substances, but contains no 
appreciable hardness, or where it is desired to retain its hardness so as not to lose 
