INDUSTRIAL AND EYGINEERING CHEMISTRY
1074
solids phase. It is apparent from Figure 3 that the portion of the total nitrogen in the latex which appears in the crepe is nearly 60 per cent. As a rule, acid coagulation results in the inclusion in the crepe of all the nitrogen intimately associated with the rubber fraction in addition to 57 per cent of the nitrogenous material normally dispersed in the latex serum. TABLE 11. NITROGEN CONTENT O F CREPED LATEX YoTotal Solids of Latex
Yo N in Creped Rubber
% T o t a l Solids of Latex
% N in Creped Rubber
44.7 41.6 40.6 38.6 38.3 38.2 37.4 32.5
0.42 0.35 0.37 0.35 0.36 0.40 0.42 0.41
30.9 29.5 28.8 28.5 27.5 27.2 24.7 24.0
0.47 0.51 0.50 0.52 0.56 0.58 0.55 0.66
VOL. 32, NO. 8
show, furthermore, that 0.577 gram of nitrogen was in the samples removed for analyses. The 4.333 grams of nitrogen in the final cream and the sera, combined with the 0.577 gram of nitrogen in the samples, sum up to 4.910 grams, a satisfactory accounting for the 4.970 grams of nitrogen in the original latex. The data presented show that the latex coagulated by acid must have a varying nitrogen content in the coagulum dependent upon the total solids of the original latex. Also, the data show that for uniformity it is essential to bring about this coagulation under the same conditions-that is, with the same total solids content. It may also be noticed that the nitrogen in the crepe varies more as the total solids content of A
A. ON LATEX SOLIDS B.ON CREPE0 RUBBER
IO0
Nitrogen Intimately Associated with Rubber in Latices I n the paragraph just above, reference mas made to the nitrogen intimately associated with the rubber fraction of the latex. This is the nitrogen so tightly fixed on the rubber particles that i t cannot be washed off by repeated creaming operations. Creaming operations normally free the rubber hydrocarbon from soluble serum constituents. I n order to illustrate the fixed character of the residual nitrogen, a typical set of creaming data are presented. The data of Table I11 show nitrogen distribution in latex, serum, and cream fractions throughout four consecutive creaming operations.
~
5 .75
?:h.j$ 0 W
a
30
I 40
50
X TOTAL SOLIDS OF LATEX
TABLE111. NITROGEN DISTRIBTJTIOK IN LATICES Tptal % N of Grams of N Associated .U in with 100 G . Grams of Solids Sample Sample Sample of Sample (Wet Basis) Sample of R u b b e r 1st serum 1287 6.53 0.228 2.930 ... 0.078 0.670 ... 859 2.70 2nd serum 0.029 0.181 ... 625 0.763 3rd serum 0.012 0.066 ... 4th serum 549 0.798 Original 4.970 0.100 latex 2524 32. 7a 0.197 1.968 0.106 60.15 0.158 1st cream 1243 58.8 0.092 0.960 0.102 2nd cream 1046 3rd cream 923 55.1 0.072 0.667 0.106 0.486 0.108 57.7 0.067 4 t h cream 726 The latex was 39.7570 in total solids content before treatment with creaming agent and dilution a t the beginning of the creaming operation; the value 32.7% is for the latex as i t was ready for t h e creaming step.
Calculation of Nitrogen Associated with Rubber An example is given to clarify the calculation procedure for those unfamiliar with creaming operations. The residual nitrogen in 100 grams of first cream is calculated as follows: One hundred grams of the first cream contains 60.15 grams of solids and 39.85 grams of water. The cream may be considered as consisting of rubber particles suspended in the first serum fraction. With the first serum analyzing 6.53 per cent solids, it follows that 100 grams of cream contain 39.85 X (6.53/93.47) or 2.78 grams of serum solids. The total serum in 100 grams of cream is then 2.78 39.85 or 42.63 grams. The nitrogen content of this serum is 42.63 X 0.00228 or 0.097 gram. The serum nitrogen, 0.097 gram, subtracted from the total nitrogen in the cream, 0.158 gram, leaves 0.061 gram of nitrogen associated directly with the rubber fraction of the cream. This rubber fraction amounts to 60.15 - 2.78 or 57.37 grams. It follows that (0.061/57.37) X 100 or 0.106 gram of nitrogen is associated with each 100 grams of rubber in the cream. This value of approximately 0.1 per cent nitrogen is in good agreement with the data of McGavack ( 2 ) determined in a somewhat different manner. The nitrogen found in the four serum fractions and in the final cream fraction totaled 4.333 grams. Sample records
+
the latex decreases, whereas a t a total solids content of from 34 t’o40 per cent the slope is not so great. Hence there will be less variation in the crepe prepared over this range than there would in the crepe prepared from latices below 34 per cent total solids content. Rubbers a t various points along this curve have been examined. The results on the characteristics of such rubbers will be reported a t a later date.
Acknowledgment We want to thank the Plantations Division of the United States Rubber Company for help in obtaining part of the experimental data. Literature Cited (1) Arise, Arch. Rubbercultuur, 4, 30 ( 1 9 2 0 ) ; 8, 425 (1924). ESG.CHEY.,31, 1509 (1939). (2) McGavack, IND.
PRESENTED before the Division of Rubber Chemistry a t t h e 99th Meeting of the American Chemical Society, Cincinnati, Ohio.
Correction-Thermodynamic Properties of Fluorochloromethanes and -Ethanes In the fifth paper in this series, “Heat Capacity of the Liquid and Vapor of Three Fluorochloromethanes and Trifluorotrichloroethane”, which appeared in the July, 1940, issue of INDUSTRIAL AND ENGINEERING CHEMISTRY, an unfortunate error appears on page 979. The equation for CJC. at the bottom of the second column should read:
R. C. MCHARNESS
