Pet ref action found at Eaft Lothian. 49 
great a proportion of vitriolic acid be left in the mixture, 
it may do more mifchief than the iron can do good. 
With this caution it were perhaps much to be wilhed, 
that experiments !h> fhould be made, and attended to, for a 
long courfe of years ; for without fuch continued and re- 
peated trials, it will be impoffible to determine in what 
manner the application may be made with moft advan- 
tage. 
I have only therefore to add, that what has been faid 
may perhaps receive fome further confirmation, from 
confidering that the chief conftituent parts of all cements 
for ftone are always lime and iron‘d; and that any experi- 
ments made in confequence of thefe obfervations will be 
likely to fucceed more rapidly in warm climates than in 
colder ones. 
Whatever there is of inaccuracy in this lhort paper 
will I am perfuaded meet with indulgence both from 
you and from the Society, whilft whatever truth is 
brought to light thereby will be receiyed and adopted. I 
therefore venture to deliver it into your hands without 
hefitation. I am, 8ec. 
(h) The ages of modern buildings are eanly known, and there are none but 
what have iron rails or bars about them expofed to the weather. If the rain 
drops from them on Portland or any gritty ftone, it becomes harder. The 
length of time fuch ftones have been fubje£ted to this procefs may eafily be 
known, and the effefts produced in them may be verified by repeated compan- 
ions of different fragments. 
(i) See croustedst’s Mineralogy, p. 45, 
Vol. LXIX. H 
1 have 
