On natural and artificial Puzzolanas. 
119 
very valuable ; I am inclined to believe, also, that the presence of the oxydeof Iron 
promotes the decomposition of the natural hydrates . This is a point which compa- 
rative experiments, undertaken at the same time on white and on coloured clays, 
would soon have cleared up. 
Science is still in want of a pood monography of clays, which, however, would 
he useful to the numerous arts in which clays are employed. The earthy com- 
pounds to which this name is given appear to be formed in a very variable manner. 
Chancehas greatly assisted me by offering two of their most important modifica- 
tions in the hydrated c ays , rich, nevertheless, in silica, and in the clays which are 
not hydrated. I have found but a small number of the latter, but I can point out 
where they are to he found, and show specimens of them. 
The precdfiing considerations appear to me to contain the rational theory of argil- 
laceous puzzolanas, which may be stated very generally as follows The consoli- 
dation of puzzoluna-mor tars under water , depends on the combination which takes 
place between the lime and the silica , on the one hand , and between the lime , alu- 
mina and oxyde of iron, on the other. It is known , moreover, from direct experi- 
ment, that these two combinations possess very rapidly the property of hardness un- 
derwater , or, ivhat is tantamount , of forming a solid hydrate in determinate propor- 
ions. 
More than one useful application of the experiments above mentioned may be 
made in a large way. First, since fifteen minutes of a beat not exceeding a dull 
red are sufficient to effect the conversion of hydrated clays into excellent puzzolanas 
when these clays are in the state ot fwwder, I believe there would be generally a vast 
economy in preparing artificial puzzolanas in this manner in open air, as recom- 
mended with reason by General Treussart : thus we should avoid having to pul- 
verize it, and we should abridge at least nine-tenths of the time and expenses of 
calcination ; in a word, we should thus calcine all clays as readily as sands ( arenes ) 
themselves are calcined*. Might we not also render useful as puzzolanas the re- 
sidues of the alum manufactories, which must be rich in excellent silica ready 
prepared, and the price of which is little or nothing? I give these ideas to those 
who, like myself, may have more than one occasion to make a useful application. 
II . — On Boring for Water. 
[From the Encyclopedia Metropolitana, Art. Boring.] 
The practice of boring for water, and the frequent success that has lately attend- 
ed the operation, in producing a great supply without the actual sinking of a well, 
render the subject one of great importance ; we conceive, therefore, that our readers 
will be gratified with the following description of the process, for which we are in- 
debted to the London Journal of Science, XXX I II. 
The situation of the intended well being determined on, a circular hole is gene- 
rally dug in the ground, about six or eight feet deep, and five or six feet wide. 
In the centre of this hole, the boring is carried on by two workmen, assisted by 
a labourer above, as shown in the plate. Fig. 1- The handle, Fig. 2. having a female 
screw in the bot tom of its iron shank, and a ring at top, is the general agent to 
which all the boring implements are to be attached. A chisel. Fig. 3. is first em- 
ployed, and connected to this handle by its screw at top. If the ground is tolerably 
soft, the weight of the two workmen bearing upon the cross bar, and occasionally 
f 
• I have executed these calcinations in a large way, in a manner as convenient 
as it is rapid, in small furnaces, supporting a kind of evaporating basin, the bottom 
of which, in strong sheet iron, was kept at a temperature near to a dull red, by the 
reversed flame of a fire-place suitably disposed. I shall give elsewhere a detailed 
description of this apparatus. 
l< Puzzolana, a kind of substance formed of volcanic ashes, moreorless compact- 
ed together, and so called from Puzzuolo, and pulvis Puteolanus, from Puteoli,. 
situated near Mount Vesuvius, from which these ashes are ejected, and in the vi*» 
cinity of which they abound.”— iocs’s Cyclopedia * 
