S6 Iron , 
Pour on it in a glass tumbler half an ounce by measure (by 
means of the common graduated measuring glasses used by 
apothecaries and chemists) of common spirit of salt, to 
which add twice as much water. Expose it to a heat 
nearly boiling for half an hour. If there be no effervescence, 
there is probably no limestone. If there be, continue to add 
by small degrees, spirit of salt and water, till all efferve- 
scence is fairly over. Let it stand 3 or 4 hours. Then add 
half a pint of water, stir it well, and filter the whole through 
(unsized) filtering paper. Wash what remains on the fil- 
ter, with half a pint more of water, and add the filtered 
liquors together. This will dissolve all the limestone 
earth, and perhaps some of the ore, and a small portion of 
the argillaceous earth, but these last are of no consequence* 
Then add to the filtered solutions, two drams by mea- 
sure of oil of vitriol, which will throw down the limestone 
earth in a thick sediment in the form of gypsum or sulphat 
of lime. Let it rest, and add a few drops more of the 
oil of vitriol, until no fresh sediment any longer appears. 
Pour off the supernatant clear liquor : add half a pint of 
hot water, and filter ; wash the filter with two more half 
pints of hot water, until the liquor that passes through, is 
no longer sensibly acid. Let the filter remain to drain for 
24 hours. Scrape off all the sediment, put it in a cup or 
a saucer to dry for at least six hours on a common iron 
stove, or 120° of Fahr. let it so remain till dry and pow- 
dery to the touch ; when 150 grains will designate 100 grains 
of limestone. Or else (which is more accurate) expose it 
for half an hour in a crucible to a red heat, when 135 
grains will designate 100 grains of limestone. 
The limestone may be generally, ascertained also, by 
means of the air it contains, but it requires some little 
knowledge of pneumatic chemistry. Thus, weigh a com- 
mon pint decanter, that will hold a full pint. Balance it 
lathe scales, Put into it, lib. avordupois weight of water* 
