1120
Vol. 15, No. 11
I N D U S T R I A L A N D ENGINEERING CHEiWISTRY
I n order to have these plate current variations as great as possible for a minimum grid voltage change, the constant grid potential for any fixed condition of the system should lie on the steepest portion of the grid-voltage-plate-current curve of the electron tube. Such a set of curves for the tube used in this work is shown in Fig. 2. The plate voltage was 23.7 volts and the filament current 1.1 amperes. This gives a desirable grid voltage swing or variation from - 1 to +1 volt, on the steep portion of the plate-current-gridvoltage curve.
.6
.4 .2
3.0 .6
Plate Current(mi1I i amps ).
-
8
Grid Current (micro-amps 1 .2
3
-f
-
I - ( t 1
2 +1
3
4
S
6
7
8
Grid Potential (volts)
10 10
20 10 20 20 20 20 20 20 20 20 20 30 30 30 40 40 40 40
40 40 40 40
GalvaVOLUME 0.01 N SILVERnometer NITRATE Swing in Observed Calculated Scale , cc cc. Cm. Av. 10.00 10.0 5.4 Av. 20.10 20.0 4.6 Av. 5.00 5.0 5.0 Av. 3.20 3.33 5.0 2.60 2.5 6.0 5.10 5.0 5.7 2.60 2.5 6.2 5.15 5.0 5.0 5.10 5.0 5.5 4.10 4.0 10.6 3.00 2.87 5.2 3.05 2.87 3.7 3.00 2.87 4.0 3.05 2.87 4.5 3.10 2.87 4.3 2.15 2.00 4.5 3.20 3.00 3.6 3.10 3.00 3.6 3.10 3.00 3.4 2.80 2.7 3.9 2.80 2.7 3.9 2.90 2.7 3.7 2.80 2.7 3.8 Av. 2.10 2.0 3.2 (Av. 7 expts.) 1.70 1.6 3.0 1.75 1.6 3.0 1.70 1.6 3.0
.
I ,
FIG.2
RESULTS To show the working of this method, a tabulation of a typical set of results will be most convincing. A salt solution is titrated whose strength in salt is continually diminished. The amount of this solution is listed, and the variation of the galvanometer indicated. Solutions varying in strength from N/100 to N/2500 are listed. This means a variation of the salt concentration from 5.85 mg. in 10 cc. of 0.01 normality t o 0.936 mg. of salt present in 40 cc. of 0.0004 normality. I n all titrations the galvanometer makes the most of the swing noted on the addition of last three or four drops of the silver nitrate added t o effect the end point. This is in accordance with the theory of the concentration cell. Ordinary colors in natural waters give no interference with this method. The end point could be more accurately attained on known solutions than with the potassium chromate indicator. This removes the personal equation in the observance of color. I n Expt. 21 the salt solution was colored with methyl blue. I n Expt. 23 the end point with potassium chromate was distinguishable only a t 5.8 cc.; in Expt. 24, 4.7 cc.; Expt. 37, 4 cc.; and Expt. 39, 3.6 by the same method. The values in Column 5 are calculated for pure salt in distilled water. Where faucet water was used for volumes
Solution Volume Cc. 10 20 10
With a N/2500 salt solution, 1 cc. of N/1000 salt solution is equivalent to 25 cc. of N/2500 strength. So 40 cc. of N/2500 are equivalent to 1.6 cc. of the N/100 strength. The faucet water used to make up the solutions required between 0.3 and 0.4 cc. N/100 silver nitrate, and gave a visible turbidity of silver chloride. The agreement is thus sure to be close enough to establish the accuracy of the method. Even with 40 cc. of tap water, the galvanometer gave a readable deflection of 0.7 cm., which goes to show the extreme sensibility of the method. The galvanometer variation from Expts. 36 to 54-N/1000 t o N/2500for average of 40 cc.-is only about 1-cm. scale. The decrease in sensibility of the calvanometer is very slow as dilution proceeds. Work along these lines will be pursued in this laboratory.
10
4
TABLE I-TITRATION VALUES
Salt Expt. Strength 1 t o 11 N/100 12. 13 N/100 14, 15 N/200 16,18 N/300 I9 N/400 20 N/400 21 N/400 22 N/400 23 N/400 24 N/500 25 N/700 27 N/700 28 N/700 29 N/700 30 N/700 33 N/1000 36 N/1000 37 N/1000 38 N/1000 39 N/1500 40 N/1500 41 N/1500 N/1500 42 43 t o 51 N / Z O O O 52 N/2500 53 N/2500 54 N/2600
5.8
vp=23.7
of 30 to 40 cc. salt solution titrated, these values should be increased by 0.3 to 0.4 cc. to account for chlorine in natural water. In Expts. 43 to 51 it took 0.3 cc. more silver nitrate, or an average of 2.7 cc., to get red color with silver chromate. Faucet water was used instead of distilled water, as an estimation of total chlorine in salt added plus that in the natural water was desired.
Use of Glue in Paper Coating I
The Bureau of Standards is conducting some experiments on the use of glue in coating paper. During the past month nine runs have been made on the experimental coating machine, using two makes of bone glue for eight of the runs and a French casein glue for one. The clay used for all runs was Lee Moor, a good grade of English coating clay. The results indicate that the water resistance of glue-bound coating containing chrome alum compares favorably with that of casein-bound paper containing no formaldehyde. It is believed that the degree of waterproofness will prove sufficient for most of the papers used for halftone printing. Difficulties have been experienced in obtaining a uniform coating, because of variation of the fluidity of the coating mixture and mechanical defects in the machine, so that additional work will be necessary before paper suitable for printing test can be produced.
The sum of $1500 has been placed a t the disposal of the College of Agriculture of the University of Wisconsin by the Sewerage Commission of the City of Milwaukee for the establishment of a fellowship to study the best methods of using activated sludge as a fertilizer. This material is prepared in large quantities as a by-product in the disposal of Milwaukee sewerage. 0. J. Noer has been appointed to the fellowship, which will be under the jurisdiction of the soils department.
