Vol. 13, No. 9
T H E JOURiVAL OF I N D U S T R I A L A N D E N G I N E E R I K G C H E M I S T R Y
816
cent by volume (g. per 100 cc. of solution) of salts in aqueous solution by the aid of the immersion refractometer. The methods are applicable to single salts; mixtures of two salts, one of known and one of unknown concentration; mictures of two salts, both of unknown concentration ; mixtures of three salts, one of known and two of unknown concentration.
The per cent by volume of salt in aqueous solution necessary to cause a change of one scale division on the immersion refractometer has been worked out €or several salts. The effect of 1 per cent by volume of salt upon the deiisity of an aqueous solution a t 20°C. was determined for several salts.
Influence of Certain Organic Accelerators on Vulcanization of Rubber' By George Stafford Whitby and Osman James Walker SCCQ L L UN V%RS TY, LTONTRBAL, C.4NADA
The experiments recorded in this paper refer to the influence of 1 per cent of ( a ) piperidine piperidyl-dithiocarbarnate; ( b ) hexamethylenetetramine, and ( c ) thiocarbanilide on the rate of vulcanization of a 9 0 3 0 rubber-sulfur mix and on the tensile properties, vulcanization coefficients, and aging qualities of the vulcanizates produced. The rubber employed was pale Hevea cr8pe. The stocks were sheeted out to a thickness of about three-sixteenths of an Vulcanization was done in a n oil bath provided with suitable stirring arrangement^.^ The rubber was enclosed in a mold consisting of two steel plates, the upper plate being 0.5 in., and the lower one, which contained a cavity for the reception of the rubber slab, being 0.8 in. thick. The upper and lower parts of the mold were fastened together by means of ten bolts and nuts, a thin gasket of lead foil and a small a,mount of a litharge-glycerol paste being used to secure oil-tightness. I n order to allow f o r the heating u p of the mold, the oil was raised, before the mold was introduced, to a temperature 20" above that at which it was desired to carry out the vulcanization. After vulcanization, two dumb-bell test pieces were cut Srom each slab. One of these pieces was subjected to a tensile test after 3 days and the other 7 mo. later. F o r carrying out the tensile tests, sliding steel wedge-shaped grips, short enough to allow of the ends of the test piece projecting beyond the grips, were employed.' The dead weight method was used f o r applying the load. The loading was done in a uniform manner, measurements of elongation being made, on gage lines; a t definite intervals. Stressstrain curves were plotted. The results obtained are shown in the accompanying tables and figures. The main series of vulcanizations on each mix was done at 141" (40 lb. steam). I n the case of the control mix and of the mixes containing hexamethylenetetramine and thiocarbanilide, respectively, vulcanizations were also carried out at a higher temperature, vuiz., 148" (50 lb. steam). I n the case of the mix containing the piperidine salt, a second series of vulcanizations was carried out a t a lower temperature, %iz,,130" (25 lb. steam), the rate of vulcanization being too high to allow of accurate experiments a t 148". P, represents the breaking stress in lb. per sq. in.; L B the percentage length at break; P, X L B /loo, the tensile Presented before the Rubber Division a t the 61st Meeting o i the Arneciaan Chemical Society, Rochester, h-.Y . , April 26 t o 29, 1921. I n the preparation of this compound the pipsridine can conveniently be applied in the form of a n aqueous solution. 3 The authors are much indebt,ed to X l r . W. B. Wiegand for making the mixinga. 4 T h e oil used was EI light engine oil known in t h e Standard Oil system as Zone Oil. ' Cf. G . Staffmd Whitby, "Plantation Rubber and the Testing of Rubber," Igzo, 261, Longmans. a I n order to obtain these lines fino they were drawn while the rubber was stretched to twice its length. After his stretching the rubber as allowed t o rest for some time before being tested.
product divided by 100, i. e., the breaking stress referred to the cross section at failure, on the assumption that the volume remains unchanged ; L,,o, the percentage length at a load of 750 lb. per sq. in. ; V. C., the vulcanization coe8cient. The stress-strain curres are shown only from a point corresponding to a length of about 400 per cent, as the later portion of the curve is the portion which can be determined most accurately and is all that is necessary in order to obtain the desired information as to relatire rate of curve, breaking points, etc. The curves referring to tensile tests made 3 days after vulcanization are drawn with unbroken lines ; those referring to tensile tests made after aging 7 mo. with broken lines. LTs0forms a convenient reference point, the figures corresponding t o which enable the relative positions of curves corresponding to different periods of vulcanization and the shifting of the curves on aging to be read easily. TABLEI.-COSTROL TIYE, Min.
P
I,
B
B
(90
P
P A R T S RUBBER
x",
100
v, c.
;53
: 10 P A R I S S U L F U R ) . After Aging 7 1110s. P L pB x", v
",,
B
B-
. ~
100
At 1410 A B
C D
120
875 150 1160 180 1290 210 B r i f.tle
970
8487 9 5 1 930 10788 866. 8 7 5 11288 8 0 0 ( b r o k e a t 150 lb/sq.
2.27 A 1 1 0 4 0 9 3 0 9 6 7 2 8 8 8 2 . 5 6 3.27 B ' 1 2 8 5 8 8 0 1 1 3 3 5 8 1 3 3 . 5 9 4.31 C ' 1 2 8 0 8 2 7 1 0 5 8 5 7 5 4 4 . 2 6 4.97
1U.J
E F
75 90
930 1261
TABLETI.--COSTROL
At 148" 9 1 3 2.97 E'1070895 SO2 4.41
8835 11008
950 880
+
1
95768363.23
PER CEST PIPERIDINE PIPERIDYL-DI~HIOCARBAMATE)
A f t e r Aging 7 mos.
G
H I J K L hf
2P
10
15 li.5
22.5
1125 1220
1315
30
1526 1870 1826
45 60 75 90
1291 1667 1687 1654
25
TABLE111.-(
824
102il 11017 11440 12760 16801 15047
At 141O 8 4 8 1.88 8 2 7 2.09 795 2.70 744 ? . 6 s 723 3 72 702 4 4 0
G'1500878131707i9203 H' 1457 8 5 3 12428 745 2.43 T'1420815115707302.91 J ' 1 8 0 3 805 1 4 6 l 0 6 8 3 4 . 0 0 I
