[ i6i ] 
Received November 1 2, 1772. 
XIX. Experiments upon the different Kinds of Mark found in Staffordshire, by William Withering, M. D Communraicl 
by Charles Morton, M. D. Sec. R. S. ’ ' 
Read Feb. 4, 1773. 
flj 
Defcription. 
. 
Quantity of cal- 
carious earth in 
half a dram, as 
feparated by the 
nitrousacid,and 
precipitated by 
What was left after the foregoing reparation, was 
no longer adted upon by the nitrous acid ; but 
One dram of each of the marles bcinc 
B 
3 
£ 
- 
- ' ' 
mild fixed al- 
kaly. 
being 
calcined, weighed 
Grains. 
Mixed with water, became 
When burnt 
Grains. 
Loft grains. 
8 
Burnt to 
’1. 
Red and blue intermixed, in fmall friable lumps. 
1 
Uniform and plaftic. 
A hard red brick. 
5 2 
5 3 
Red brick. 
2. 
Red, in fmall friable lumps. 
Grey, in large hard lumps. 
Uniform and plaftic. 
A hard red brick. 
7 
Red brick. 
3- 
5 
Plaftic, but a little gritty. 
A foft yellowifh brick. 
49 
1 1 
Soft yellow brick. 
4- 
Red, hard, compadl. 
3 
Uniform and plaftic. 
A hard red brick. 
5° 
1 6 
Red brick. 
5- 
Red, with grey fpots, in large hard lumps, fcarcely to be broken with a hammer. 
Light grey, like a grit Hone. 
Brown, friable, in large lumps. 
H 
Plaftic. 
A' foft pale red brick. 
48 
12 
H ird grey ftone. 
6. 
8 
Gritty, no union. 
No union. 
5' 
9 
Soft and llony. 
7 • 
18 
No union. 
A little cohefion. 
46 
14 
Soft ftone. 
8. 
Red,- in large friable lumps. 
H 
Plaftic, but a little gritty. 
A foft red brick. 
48 
1 2 
Soft ftone. 
9- 
Brownifh white, very hard, like calcarious incrullations. 
16 
No union, gritty. 
No union. 
43 
j 7 
Soft ftone. 
10. 
Lead colour, friable, flaky. 
Hi 
No union, gritty. 
No union. 
48 
12 
Soft ftone. 
1 1. 
Brown grey, very hard, in irregular lumps. 
16 
No union, gritty. 
No union. 
40 
20 
Soft ftone. 
12. 
Lead colour, in powder and in fmall hard lumps. 
20§ 
Uniform and plaftic. 
A foft whitifh brick. 
2 9 
3 1 
Powdery. 
The calcined 
marles put into 
water, produced 
Mo effedl. 
No effedl. 
Weak lime water. 
No effedl. 
Lime water. 
Lime water. 
Lime water. 
Strong lime water. 
Strong lime water, 
Strong lime water. 
Strong lime water. 
Strong lime water. 
the lead, N° 12 the mod. The effervefcence having 
To the filtered colours was gradually added mild fixed 
Half a dram of the marles being put into fimilar glafs cups, two drams of nitrous acid being added to each glafs, they all effervefeed ; N° 1 and 2 
ceafed, and fix drams of rain water being added to each glafs, the liquors were all filtered, and after filtration, changed violet paper to a red colour, 
alkali, fufficient to faturate the acid, and precipitate all the earth it had diffolved. The precipitated earth being wafhed in rain water, till free from all faline matter, weighed, when dry, as in column the 
third. Column the fourth fhews that, after the reparation of the calcarious earth, there remained in N° 1, 2, 4, a red clay ; in N° 12 a white clay ; in N° 8 a red clay, and a portion of fand ; in N° 3 a 
whitifh clay, with a portion of fand ; in N° 6, 9, 10, 11.- pure fand ; and in N° 7. fand, with a fmall portion of clay. Thefe refiduums were all wafhed with rain water before they were burnt. The pre- 
cipitated powders being mixed together, 82 grains thereof put into a crucible, and calcined with a ftrong hear, loft 35 grains in weight. Rain water was poured upon the calx ; the next morning there was a 
pellicle upon the furface of the water; it tailed ftrongly of lime, and let fall a calcarious earth, upon the addition of mild fixed alkaly. The marles were kept for feme weeks in a dry place before they were 
made ufe of. They were all got out of marie pits in the neighbourhood of Stafford, except N° 12, which is found near the Duke of Bridgewater’s canal, in a powdery form, and when mixed with one fourth 
part of : ^fclay is burnt to quick lime. All the above marles crack and fall to pieces, when expofed to the weather. 
The foregoing experiments were undertaken with a view to afeertain how far it would be advifeable to attempt burning the marles of this country into quicklime, for the purpofes of agriculture; they may 
likewife furnifh us with fome ufeful hints relative to the kind of marles proper to be ufed upon different kinds of lands. Perhaps the calcarious earth united with clay, as in N° 1, 2, 4, &c. may be the 
bell for light fandy foil; and N° 6, 9, 10, 11, where the calcarious earth is united with fand, the moft eligible where the land is already ftiff, and abounding with clay. How far the different quantities of 
fixable air, or other volatile parts, contained in each of the marles, as fhewn by column the fifth, will influence their preference in agriculture, muft be left to the experience of the farmer to determine. 
Vol. LXIII. 
Received 
