748 



SCIENCE. 



[N. S. Vol. XVII. No 436. 



This rapid succession of light blows sets up a 

 vibration in the chisel, which, with even a 

 slight pressure against the work, gives it a 

 remarkable cutting capacity. In fact a chisel 

 so driven will cut an indurated clay as rapidly 

 as an ordinary hand tool will cut chalk. 



The chisels commonly used in stone cutting 

 are made uniformly of one-half-inch square 

 or octagon steel about nine inches in length. 

 Of these one and one half inches of the head 

 end is turned down to three-eighth-inch diam- 

 eter, so as to fit into the chamber of the tool 

 and provide the shoulder necessary to hold 

 the chisel at the precise point which will 

 render the stroke of the hammer most effectual. 

 These chisels are used indiscriminately in all 

 sizes of stone hammers and are ill adapted for 

 the preparation of fossils. The requisite for 

 such delicate work is a keen stroke under com- 

 plete control. This has been in a measure 

 attained by fitting an attachment to the stone 

 cutting hammer. 



In the accompanying figure a represents the 

 plunger, h the hard steel barrel and c the 

 softer outer jacket of the hammer. A tem- 

 pered steel cylinder d is attached to c by a 

 heavy thread ; this holds in position a separate 

 tool head e, which receives the blow of the 

 hammer and bears the chisel f in a taper 

 socket. A coil spring g acting against the 

 shoulders h and i in turn receives the blow 

 of the hammer or any part of it not util- 



Q 



gy. 



Cross-section of Pneumatic Hammer, with Tool- 

 liolding attachment. 



ized in work at the point of the chisel. The 

 tool head e is fitted to a square opening in d 

 at j which prevents rotation. The taper- 

 socket holds the chisel in place so that it may 

 be guided by the hammer; when desired the 

 chisel may be readily released by placing in a 

 vise and tapping the tool head lightly. One 

 escape-vent is directed forward so as to blow 

 away dust and small chips from the work. 

 For chisels, one-fourth-inch round steel cut 

 in six-inch lengths and dravsoi to a point of 



one-eighth or three-sixteenth inch in breadth 

 are most efficient. For finishing, a broader 

 bladed chisel may be used to advantage. 



This appliance makes it possible to dispense 

 with the unnecessary weight of metal in the 

 chisel so that a keener stroke and a greater 

 cutting capacity result. At the same time the 

 manipulator is relieved of the necessity of 

 holding the chisel in place with the left hand 

 and so avoids the benumbing jar caused by the 

 vibration. 



The advantages of this hammer over the 

 old-fashioned hammer and chisel are its much 

 greater cutting capacity and its freedom 

 from the jar which causes so much breakage 

 in specimens encased in hard matrix. The 

 relative cutting capacity depends upon the 

 nature of the material to be removed. If it 

 be sandstone, by which tools are rapidly dulled, 

 blocking off in large pieces by means of ham- 

 mer and chisel will be found more expedient. 

 Or if it be a very hard substance, such as 

 quartz or chalcedony infiltrations, a method 

 of spalling by means of a square-poled ham- 

 mer may prove more efficient than either. But 

 in limestone or any of the indurated clays 

 the superiority of the pneumatic hammer is at 

 once evident. This is especially true in the 

 case of complicated specimens where there 

 are deep cavities or foramina to be developed. 

 In such work the pneumatic chisel can be used 

 wherever its point can be introduced, while 

 with the old-fashioned hammer and chisel one 

 is often at a loss for room to hold and strike. 

 The cutting capacity of a chisel is much 

 greater also when used with the pneumatic 

 hammer, as the point can be made much 

 harder without danger of breaking. Chisels 

 made from a high grade English steel of 

 1.4 per cent, carbon chilled to a file-like hard- 

 ness may be used four or five hours in con- 

 cretionary clays without need of grinding. 



The advantage of relieving the specimen 

 from the jar of the hand-hammer can scarcely 

 be overestimated. In working out dinosaur 

 vertebrffi from a concretionary matrix by 

 means of hand tools we have often found it 

 necessary to break the specimen to pieces 

 with a hammer in order to remove the chal- 

 cedony-filled masses of concretion from the 



