238 Scientific Intelligence. [Mancu, 
have cut out an evaporating dish of the shape required. A little 
practice will enable the operator to cut the glass neatly and readily. 
Lavoisier’s method was to surround the flask or retort at the part 
to be cut. with a red-hot iron ring, and then to wet the part... This 
method is probably good enough (indeed I have sometimes used it) ; 
but it would require a separate ring for every size of flask or retort 
to be cut. On this account it is inferior to the method which J 
have described. 
IX. Query respecting the Mode of removing common Putty from 
lass. 
(To Dr. Thomson.) 
SIR, 
_ Ihave read somewhere of a chemical preparation or process by 
which the putty that fastens the squares of glass in a window can be 
decomposed, or its adhesive property destroyed, so as to permit re- 
moval of the glass without the risk of breaking. If you, or any of 
your Correspondents, will be so kind as to communicate the method 
by which this is accomplished, or point out any publication from 
which the information may be obtained, it will very much oblige 
Arbroath, Fun. 2%, 1816, A Constant READER. 
Answer.—Common putty is nothing but a paste made of chalk 
and lintseed oil. Hence it is readily softened and removed by the 
application of any acid. Nitric acid will act most speedily ; but 
miuriatic acid may likewise be used. Indeed, if no other acid be at 
hand, the putty might be removed from the glass by vinegar, but 
the process would be tedious. Even alkaline leys would have con- 
siderable effect by acting upon the oil, though they would not 
answer so well as acids. 
X. Greywacke to the North of the Forth. 
(To Dr. Thomson.) 
DEAR SIR, 
On reading your very highly interesting Account of the Improve- 
ments in Physical Science during the Year 1815, in the Annals of 
Philosophy for this month, I observe, under the head of Geognosy 
(p. 65), the following sentences: “ Next to the primitive come the 
class of rocks called dransition. They contain petrifactions, and 
are very abundant in Great Britain. 1 do not know that they have 
been observed further north than the Frith of Forth.” 
You will, I know, excuse me when I put you in mind of what 
you have, amid your multifarious engagements (and no wonder), 
happened to overlook. Lallude toa short paper of mine, entitled, 
Mineralogical Observations in the Highlands of Scotland, obligingly 
published by you in the Annals of Philosophy for July, 1813, Art. 
‘VII. By turning to that article, you will find that in August, 
1812, Mr. Tardive and myself discovered greywacke north of the 
Frith of Forth. Near the beginning. of the paper referred to are 
