134 Blasting of Rocks—Dangers and Remedies. 
If. Letter of Mr. Blake. 
Whitneyville, September 5, 1829. 
TO PROF. SILLIMAN. 
My dear sir—In blasting rocks, as you know, it is not an uncom- 
mon thing for explosions to take place before the charging is completed. 
Almost every year some of our numerous newspapers give accounts 
of such premature explosions, attended with fatal consequences to the 
operators. ‘The cause of the accidental ignition of the powder in these 
cases, is sometimes Clearly indicated by the known circumstances of 
the case, and at others it ean only be referred to the unknown circum- 
stances, which may have attended the operation. I have read with 
attention the letter on this subject, which you did me the honor to 
refer to me, which was addressed to you by Dr. B. H. Catlin, of 
Haddam, giving an account of an accident of this kind, and soliciting 
information as to the cause of the ignition of the powder and the 
means of avoiding similar aecidents in future ; and shall now with 
pleasure proceed to state to you my views of the subject, as you 
desired. 
The method of charging the rock in this case, as minutely descri- 
bed by Mr. Catlin, was that which is now most generally practised, 
and it is perhaps the only method that was in use twenty years since. 
The workman appears to have used more than the ordinary degree 
of caution; and I cannot see that there was any thing in the case to 
produce axploaon. which is not liable to exist, in every case, im which 
this method of charging is practised. In the Journal of Science, 
Vol. XII. p. 161, are given the results of some experiments tried by 
M. Aubert, which go to show that violent shocks and percussions; 
between any two hard substances, may occasion the disengagement 
of sufficient heat to inflame gunpowder; and it is well known that 
violent attrition is still more favorable to the disengagement of heat 
than percussion. To both of these the process, as described by Mr. 
Catlin, is evidently in some degree liable. In tamping down the first 
quantity of gypsum, which was put in next above the wad, the irreg- 
ular pressure of those pieces which were in contact with the wad, 
would be very liable to force the wad down on one side of the hole 
or in the centre, which would cause the powder to be thrown up 07 
the other side or on all sides. The spindle is usually inserted into 
the powder on one side of the hole ; consequently the wadding would 
not be likely to close the hole Searels around the spindle, and the 
