102 TOUCHWOOD TINDHR-BOX. 



choking, (hat snff.-r- only a pait to escape, while the column rest 

 ing on the area of the ;HSIOM is pushed entirely toward the extre. 

 mit> ol the tube, where the a punk to he kindled lies. 



kt In the piston with a single broad groove, the area of the 

 circ-le, on which the column of uir rests, is much smaller, con. 

 gequently the column itself is less. '1 he jesistance the air expe- 

 riences in passing through the groove is next to nothing ; for we 

 heai no noise on moving the piston backward and forward ; and 

 as air expands in all directions, when the piston is moved, the 

 column resting on the area of the circl<-, resting at the same time 

 laterally on that which answers to the groove, it recedes f. <>in all 

 the points of contact, and flows entirely through .the channel it 

 finds opens. It is so true, that it wholly flows out, that the 

 piston, when it touches the extremity of the tube, remains there; 

 while with other pistons a sufficient quantity of air is retained to 

 occasion a spring and repel them. 



u I think it proper to say a word or two on the quality of the 

 spunk. The driest, softest, and least impregnated with nitre, 

 should be chosen. In that of the best quality a pi ce will not 

 always be found equally jjood throughout. Some contains a great 

 deal of nitre, and is kindled with more difficult)*. This may be 

 known by the cold taste it leav< s on the tongue; or by kindling 

 it: for when it has taken fire the nitre melts, and sometimes 

 throws out sparks, that may be dangerous when they spirt out of 

 the instrument, particularly if made with a cock. As it is usual 

 to blow on the spunk, to try whether it be kindled, a spark may 

 be thrown from it into the eye. This painful accident once hap. 

 pened to me. 



" They who imagine that electricity kindles the spunk, consider 

 these sparks as an incontrovertible proof of their opinion. I think 

 they are mistaken in this case; yet I must not conceal a fact com. 

 municated to me by Mr. Veau-Delaunay, which sec ms to confirm 

 this opinion, of which he is a partisan. Out of twelve times, when 

 he operated with the instrument without any spunk in it, he saw 

 sparks emitted three times. There are strong reasons, however 



The common spunk of the shops is prepared from agaric, which is fint 

 boiled in water ; beaten well when dry ; steeped in a strong solution of salt- 

 petre ; ;iii(l I i-ils drii d in an oven. If ihe solution of nilre be too strong, the 

 agaric is loaded with (his salt, which retards its inflammation. 



