IY ANNUAL REPORT 
I. From what we know of pozzuolane materials we realize that 
their hydraulic value depends on the amount of available silica present, 
that is, silica soluble partly in hot hydrochloric acid and completely 
soluble in a hot solution of sodium carbonate. A complete analysis is 
required in. but few cases, and is of little value except where some irreg- 
ular constituents are making their influence felt. 
The complete analysis of a pozzuolane is carried on, as is customary 
for silicates, by fusion with sodium carbonate, separating the silica, 
alumina, iron, calcium oxide and magnesium oxide as is done for clays, 
the method of analysis of which will be given later on under the proper 
heading. 
2. The soluble silica is determined as follows. Treat one gram of 
the sample with 4o cc. of hot dilute hydrochloric (1: 2) acid in a casserole, 
boil for five minutes, dilute to 150 cc. with boiling distilled water and 
keep boiling for 15 minutes. Now filter the liquid off through a hard- 
ened filter, wash several times with hot water, and rinse any residue 
which got on the filter back into the casserole. To the residue now 
addy SO ce Ota. Solution econtalninow era erann  OlmMcatisnicms ode 
and 3 grams of sodium carbonate. Heat on a hot plate or water 
bath, for 60 minutes, but do not boil. Filter through the same hardened 
filter as before and return any residue transferred to the filter to the 
casserole. Add now 50 ce. of the alkaline solution, of half the strength 
given above, and heat for 30 minutes. Filter as before and repeat this 
treatment at least twice more, till no more flocculent silicic acid is 
detected in the filtrate on testing with ammonium chloride. Sometimes 
the test is rather slow to show. In this case make decidedly acid with 
hydrochloric acid and add in the test tube a few drops of ethyl alcohol. 
Cooling the hot test solution rapidly in water accelerates- the reac- 
tion. To the residue in the casserole add 10 cc. of the hydrochloric 
acid, dilute to about 50 cc., heat to boiling, filter and wash almost free 
from chlorine with water containing about 10 per cent. of ammonium 
nitrate and a little alcohol. The total filtrate is now made distinctly 
acid with hydrochloric acid and evaporated to dryness in a porcelain 
or, preferably, a platinum dish. The residue is now heated in a hot air 
oven, best lined with clay tiles, at 120° C., till fumes of hydrochloric 
acid are no longer detected. Take up in a little hydrochloric acid, add 
boiling hot water and filter on an ashless filter. The filtrate is returned 
to the dish in which evaporation.took place and is again boiled down 
to dryness and heated at 120° C., say for one hour.. Take up again in 
acid and hot water, filter on same filter and wash practically free from 
chlorine. Ignite and weigh as silica, SiO,. Final ignition must take 
place over a blast lamp. It is also advisable to test the purity of the 
silica with hydrofluoric acid. 
The loss on ignition often is a valuable and sufficient criterion of the 
value of a puzzuolane material, it being due to the expulsion of the com- 
