J. M. Ordway on Waterglass. 191 
Indeed, the precipitates were always found to contain at least 4 
equivalents of silica to 1 eq. of alkali. Thus, 
82—100 g. of 25 p.c. NaSi,, with 100 g. of 25 p. c. Na, As, gave 35:3 
g. of a hard pressed, opaque mass containing 44°4 p. ¢. net of NaSis-s0. 
The cause of this seemingly anomalous behavior on the part 
of the arseniate,—and the phosphate acts in the same way,—is to 
be found in the fact, long ago developed by Graham, that, in the 
so-called “neutral” arseniates and phosphates, only two-thirds 
of the proper quantity of alkali is present, and they are there- 
fore in reality acid salts. Hence, when either of them is brought 
in contact with waterglass, it appropriates a considerable part of 
the alkali of that feeble combination, and of course gelatinizes the 
silica. Indeed, its action is similar to that of a bisulphate or a 
bicarbonate. It is observable that in making the mixture no 
change takes place till so much of the arseniate or phosphate is 
added as will seize on all the soda except somewhat less than is 
needed to form with the silica Na&i,. Thus, 
$3.—100 g. of 25 p.c. NaSi,, with 50 g. 25 p.c. Na, As, suffered no vis- 
ible alteration, though it was allowed to stand two days. And here 
6NaSi,+2Na,As=2Na,As+4Nadi,. But 25 g. more of the arseniate 
Solution at once gelatinized the whole mass, 6NaSi,+3Na,As—sNa,As 
+3Nabi,. 
Of course then, to make experiments parallel to those carried 
on with chlorids, acetates, and the like, it was necessary to start 
anew and use the really neutral or normal Na,® and Na,4s. 
see salts were found to have little or no effect on any water- 
i 
34—100 g. of 25 p. c. NaSig5 gave no precipitate with 100 g., or with 
200 g. of 25 p. c. NaO. BO,. 
The following trials were made to ascertain the influence of 
temperature: 
@—The mother-liquor, heated in a water bath to 90° C., gave 16°8 g. of 
@hbard pressed product containing 51°5 p.¢. gross of NaSigga. = 
b—100 g. of 25 p.c. NaSi, and 100 g. of 25 p.c. NaCl, both boiling 
iS, Save 21 g. of a hard pressed curd containing 50 p.c. gross 
Ana 12.38, 
The mother-liquor remained clear on cooling. 
%6,a—100 g. of _c. NaSi;75 were mixed with 100 g. of 25 p. e. 
Nade,—both at the boiling point. The hard pressed precipitate, weigh- 
8 8-7 g., contained 47 p.c. gross of NaSiz4s. 
“—The mother-liquor cooled to 3° C. gave 6'1 g. of a soft deposit con- 
ding 44 p. c. gross of NaSi:93- : 
