On the Combinations of the yellow Oxide of Lead. 341 
rectness of Mr. B’s observations, and occasioned me to resist his 
conclusions, as | have done in my three Letters and Notes on 
Mr. B’s Work, in this and the previous volume of the Phil. Mag. 
Mr. Hall’s observations seem to me to render it now almost 
certain, that Mr. B. has mistaken the Ist Limestone Rock for 
the 4th, as I have often before hinted, and the result seems an 
important one ; viz. that the S/ate of Ingleborough (see vol. xlil. 
p-99 and 170) must probably be referred to the same stratum 
as the Ist Toadstone of Derbyshire! instead of a stratum under 
the 4th Limestone, as Mr. B. has contended. How far this new 
suggestion, of which I have recently added a hint, in my Note 
on page 275, may be correct, and its influence may extend to- 
wards the explanation of the real structure of the British Isles, 
I shall be industrious to inquire, and shall gladly receive the 
facts or suggestions that your Correspondents may be able to 
offer: the means for which will now I trust be greatly extended, 
by the speedy publication of Mr. Smith’s large Map of the 
Strata, which may now be seen, in part, and Prospectus ob- 
tained, by application to Mr. John Cary, No. 181, Strand. 
I am, sir, your obedient servant, 
12, Upper Crown Street, Westminster. JoHN Farey, Sen. 
To Messrs. Nicholson and Tilloch. 
LXXII. Facts and Observations towards a History of the Com- 
binations of the yellow Oxide of Lead with the Nitric and 
Nitrous Acids. By M. Cuevrevr. 
[Continued from p. 270. ] 
Analysis of the Nitrites of Lead. 
30. Tox nitrite of lead, when exposed to the sun for several 
days, retains some water, as we may see on heating.it in along 
close glass tube: that which has been exposed in a retort at the 
heat of boiling water, until no more humidity is extricated, loses 
a portion of acid. 
100 parts of nitrite which had been exposed to the sun, lost 
by heat from 19°5 to 20 of acid and water. 
Ol. As the acid of the nitrite begins to be extricated from it 
at the temperature which is necessary to separate the water 
from it, I preferred analysing a nitrite which could retain water, 
rather than trouble myself to analyse one which might have 
lost acid: I think therefore that the salt which was used in the 
following analysis retained a little water. It had been dried in 
the sand-bath with great care. It yielded 
AL ys iasmaver newest te LO 100 
Onide . Aan eh ses 81°85 450 
