April 1, 1917.] 



THE INDIA RUBBER WORLD 



389 



LABORATORY APPARATUS. 



MEASURING STRETCH OF RUBBER. TEST SAMPLES. 



nPHE ordinary testing machine is provided with a pair of hand- 

 adjustable pointers, movable on a measuring scale for determin- 

 ing stretch. The operator, with or without assistance, endeav- 

 ors with these pointers to follow the movement of the reference 

 marks on the rubber sample under test. This method leaves 

 much to be desired as to convenience and accuracy. The fol- 

 lowing substitute has been found entirely satisfactory. The in- 

 strument required consists of a pair of hard wood dividers, made 

 by fastening together, with a quarter-inch screw bolt and thumb 

 nut, two strips of wood ^ inch thick, 1 inch wide and 18 inches 

 long. The bolt should be located about 4 inches from one end. 

 The opposite arms are tapered together to a chisel edge. To 

 use the instrument the operator holds it by one short arm, with 

 the right hand, placing the thin edge of the corresponding long 

 arms on the upper reference mark of sample. Witliout further 

 attention the instrument moves downward with the upper line 

 as the sample is stretched. The operator follows the progress 



of the lower reference mark, 

 opening the dividers with the left 

 hand, keeping contact with the line 

 until the sample breaks. Having 

 to follow but one mark, the oper- 

 ator can do it easily and accu- 

 rately. The final spread of the 

 dividers, less the original distance 

 apart of the reference marks, gives 

 the actual stretch, which should 

 be recorded in terms of percentage 

 Mil length of the marked interval. 



ALUNDUM FLAME COLLAR. 



This piece of apparatus is de- 

 signed to produce uniform condi- 

 tions of intense heat for igniting 

 in alundum or platinum crucibles. These collars are made to 

 withstand wide variations of temperature. [Norton 

 Worcester, Massachusetts.] 



Co., 



METHODS OF TEST. 



THE physical testing of rubber materials as specified by the 

 Board of Estimate and Apportionment, of New York City, 

 reported in the Marcli number of The Indi.\ Rubber World, is 

 continued as follows ; 



DETEKMIXATION OF FRICTION OR ADHESION STRENGTH. 



The determination of friction or adhesion strength between the 

 rubber and the fabric, or between the layers of fabric, shall be 

 made as follows : 



Apparatus. All friction or adhesion strength tests shall be 

 made on the tensile testing machine. 



RrDP.ER HOSE AND CIRCUL.AR TEST PIECES. 



All rubber hose and other wrapped circular test pieces shall be 

 slipped on a mandrel one-eighth inch wider than the test piece 

 and of the same diameter as the inside of the hose. 



The mandrel with the test piece in place shall be slipped on tlie 

 pin attached to the povrer head. 



The free end of the test piece shall be clamped to the lower 

 head of the testing machine without twisting and centered over 

 the mandrel. 



The weight clutches shall be raised and the macliine started at 

 the uniform rate of one inch per minute. 



After separation commences the load shall be constantly 

 watched to see that it does not at any time fall below the speci- 

 fication requirement. 



On the Schopper machine this load shall be recorded on the 

 automatic recording device. 



The entire friction layer or layers shall be separated. 



COTTON RUBBER-LINED FIRE HOSE. 

 Cotton rubber-lined fire hose test pieces and test pieces of a 

 similar character shall be tested exactly as prescribed in the 

 foregoing under "Rubber Hose and Circular Test Pieces," ex- 

 cept that the fabric shall be fastened to the power head with a 

 clamp instead of a mandrel. 



PACKING AND OTHER FLAT TEST PIECES. 



Packing and other flat test pieces shall be tested exactly as 

 prescribed for rubber hose, except that a clamp instead of a 

 mandrel shall be used, and either the fabric or the rubber shall 

 be fastened to the lever head according to the thickness of the 

 rubber. 



If the rubber is not thicker than one-eighth inch the fabric 

 shall be fastened to the lever head. 



If the rubber is thicker than one-eighth inch the rubber shall 

 be fastened to the lever head. 



When fabric and fabric are to be separated, the heavier shall 

 always be fastened to the lower head. 



When heavy materials like belting are to be tested, the test 

 pieces shall consist of not more than two plies of the fabric for 

 any one test. 



DRY HEAT TEST. 



The test pieces prepared and measured beforehand are placed 

 in a hot-air oven at the specified temperature for the specified 

 time, cooled to room temperature, the tensile strength and 

 elongation tests made, compared w'ith the untreated specimen, 

 and the reduction calculated to the nearest tenth per cent. 

 GASOLENE TEST. 



Tube and cover test pieces for the gasolene test shall be cut, 

 prepared and measured as specified under preparation of tensile 

 strength. Test pieces shall be completely immersed in 57- to 63- 

 degree Baume gasolene for a period of 48 hours at a temperature 

 between 60 and 80 degrees F. They shall then be removed, 

 allowed to rest and freely evaporate in air at the same tempera- 

 ture for 24 hours. The tensiie strength and elongation tests 

 shall then be made, compared with the untreated specimens and 

 the reductions calculated to the nearest tenth per cent. 



Friction strength test pieces shall be made on a one-inch 

 specimen cut for the mandrel test. After treatment with gaso- 

 lene, as outlined above, the friction strength shall be determined, 

 compared with the untreated specimen, and the reduction calcu- 

 lated to the nearest tenth per cent. 



STEAM TEST. 



The determination of steam resistance of hose shall be made 

 by connecting three-foot lengths to a steam supply pipe and 

 maintaining the pressure required in the specification for the 

 period called for. The tensile strength elongation and friction 

 strength tests shall be made on the specimens cut, prepared and 

 measured after the steam test, compared with the untreated 

 specimens and the reduction calculated to the nearest tenth per 

 cent. 



DETERMINATION OF POROSITY IN AIR HOSE. 



The length selected for test shall be subjected to 140 pounds 

 air pressure. The cover shall then be cut lengthwise with the 

 hose for at least two feet. The pressure shall be maintained for 

 five minutes. At the end of this period the length, still under 

 pressure, shall be submerged in water. If there is a distinct 

 escape of air which is not due to the air confined in the struc- 

 ture of the walls, the hose shall be considered porous. 



DETERMINATION OF BURSTING OR PROOF PRESSURE. 



The determination of bursting or proof pressure shall be made 

 in the following manner : 



The hose shall be stretched out on a plane surface in a 

 straight line, connected to the water line or pump and filled with 



