458 Transactions,—Chemistry. 
As may be readily imagined it was a great source of trouble and expense 
to keep the pumps at work while the incrustation was forming inside them, 
and now that it has ceased forming there, I hope we shall never have a 
repetition of it. I have sent this slab thinking it may find a place in the 
Museum. 
Nore.—Specimens of this incrustation were sent to the Colonial Laboratory 
in 1875, and reported on as follows :— 
** No. 1758 is an inerustation taken from the cylinder of that large pump 
used at the Thames diggings for draining the lower levels of certain claims 
there adjoining the beach. It appeared to have incrusted a portion of this 
cylinder evenly over to a thickness of about one-quarter of an inch, and is 
very hard, also impervious to water, and presents to the naked eye an amor- 
phous appearance, except on its inner side, this being, on the other hand, 
manifestly semi-crystalline; and besides is interspersed, though somewhat 
rarely, with crystals of iron pyrites. The pyrites is in all probability how- 
ever, merely a mechanical deposit. 
“The annexed results of an analysis made of a portion of this in- 
erustation show it to be essentially carbonate of lime. As it has certainly 
been deposited in this form from some solution of it, and as the solvent for 
it in this case has most probably been water charged under a considerable 
pressure with carbonie acid it would appear that this incrustation has been 
induced by the escape of carbonic acid, caused by reducing the pressure and 
therefore the capacity of the water for carbonic acid by the action of the 
pump, resulting of coursein a lowering of its solvent power for carbonate of 
lime :— 
Analysis. , 
* Carbonate of lime .. ae 
ee «d .. 85:94 
Carbonate of magnesia  .. i. Ar $i E '84 
Iron oxides, with alumina M ee ux eee 
Siliceous matters, insoluble in weak acid  .. zs ie dB 
Soluble silica $ 44 
Water .. Mim . x 2:17 
Alkalies, sulphur, ete. 174 
