OCEAN BOTTOM— PIGGOT 213 



This is true up into that portion where the four steel webs carry the 

 force of the blow from the center axis to the walls. Near the upper 

 end of this part, the available volume increases slightly, and this fact, 

 combined with the outward slope of the outside of the walls, provides 

 a partial vacuum or cavitation — during the rapid movement through 

 the water — which removes the back-pressure from the colunm of 

 water inside the bit and provides an almost open-tube condition. 



Though the bit was frequently driven deep into mud, no samples 

 were obtained until this device was perfected. 



THE BIT 



That portion of the apparatus below the water-exit port has been 

 called the "bit." Its length determines the possible length of the 

 sample ; bits of different lengths may be used as found desirable. It 

 consists of a tube of alloy steel of 2i/4 inches inside diameter and 

 l^-inch walls. Inside it are four longitudinal lands, as in a cannon, 

 but straight. The four grooves between these lands communicate 

 with four openings to the outside at the top of the tube. Their func- 

 tion is to permit water to get down to the bottom of the bit and to 

 fill the cavity in the mud created b}' the withdrawal of the bit — i. e., 

 to "break the suction." The brass sample tube slips inside the lands 

 and fits snugly against them ; this causes the grooves to form longi- 

 tudinal channels from the top to the bottom of the bit. 



The bottom edge of the bit is provided with a cutting edge of 

 hardened tool steel, which fits loosely between the sample tube and 

 the steel tube and is prevented from falling off by two small screws. 

 However, it has a play of three-sixteenths inch — i. e., may hang that 

 far below the end of the steel tube — but when pressed up it fits snugly 

 against the end of this tube. It therefore acts as a valve, which pre- 

 vents mud from entering the grooves while the bit is being driven 

 into the bottom, but opens and permits water to flow out of the 

 grooves while the bit is being withdrawn from the mud. 



After a "shot", the brass sample tube is withdrawn, with the mud 

 core inside it, and a new one is inserted. It is cut off at the top of 

 the mud, corked at both ends, and these corks securely taped. They 

 are labeled in a manner to indicate the top and the bottom of the 

 core and may then be shipped and kept without alteration until 

 opened for examination in the laboratory. This is done by cutting 

 the tube longitudinally in two diametrically opposite places and then 

 inserting two sheets of tin in one slot and pressing them across to 

 the opposite wall. The tube may then be opened hinge-fashion and 

 the tin strips removed without distorting the sample. This pro- 

 duces two equal parts to each sample, each part lying in its own 

 brass trough, and reveals the structure of the core. This procedure 



