36 Experiments on the Adhesion of Iron SjpiJces, 



tightened by a strong screw held the spike firmly, while the appli- 

 cation of weights upon the long arm of the lever drew the timber 

 away, and released the spike. Care was taken to cause the strain 

 to pass through the axis of the spike, and, by a very gradual appli- 

 cation of weights, to avoid surpassing that force which was just suffi- 

 cient for its extraction. 



The first experiment was upon one of Burden's patent square 

 spikes, with a cutting edge, intended to be in all cases placed across 

 the grain of the timber. This spike was .375 of an inch square, and 

 was driven into a sound plank of seasoned New Jersey yellow pine, 

 3f inches. The force required to extract it was 2052 lbs. and the 

 exact weight of the part driven into the wood was 866 grains troy. 



The second trial was upon a flanched, grooved and swelled spike, 

 having the grooves between two projecting wings or flanches, on the 

 same sides as the faces of the cutting edge. The other two sides 

 were planes, continuing to the head. A cross section of this spike, 

 taken If inches above its edge or Y\a [ Fiff. 2. 



point, had the form of fig. 1. At y^ g ^ 



of an inch, that is, where the flanch- 

 es project least from the edge, or 

 where the swell between them comes 

 nearest to forming a perfect square, e e 



the form is as shown in fig. 2 ; the dotted line e e, in each figure, 

 representing the direction of the cutting edge. Towards the head 

 of this spike, the flanching and grooving is suppressed, and the form 

 becomes a square. This experiment was made on the same piece of 

 Jersey yellow pine as the first, and the weight required for extracting 

 the spike was 1596 lbs. The weight of the part driven in was 708^ 

 grains. The cutting edge was irregular ; the distance to which it 

 was driven, was 3f inches, as in the first trial. To know the rela- 

 tive value of the two forms of spikes, we have but to divide the 

 weight required for the extraction of each by the number of grains 

 in the part which had been buried in the wood ; thus, 2052-^-866 = 

 2.37, and 1596-4-708.25 = 2.112. Hence the plain spike had an 

 advantage over the swelled and grooved one, in about the proportion 

 23 to 21. It should be mentioned also, that the plain spike was 

 drawn out by a very gradual addition of force, whereas the force of 

 1596 lbs. drew the grooved spike immediately after its application. 

 In the first trial, an attempt was made to detect any yielding or grad- 

 ual retreat of the spike, before the final start, but none was observed. 



