670
T H E JOC‘RA’AL OF I N D C S T R I A L AAiD E N G I N E E R I N G C H E M I S T R Y .
a sampling pipe curved with a radius of and facing the flow of gas.
12
inches
4. The sample must be nTithdrawn where possible from a vertical pipe, or as near vertical as practicable and the sampling pipe should be inserted to such a degree
I
that the open end is in that region of the main where the mean velocity has been found to exist. CHEXICALLABORATORY,
ILLIVOIS STEELCO., SOUTHWORKS. So CHICAGO,ILLINOIS.
PLANTS AND MACHINERY A NEW ACCELERATED TEST FOR PAINTS, B y H K BESSON ASD CARL POLLOCK
Received July 20, 1911.
The ease with which iron corrodes when subjected to the action of electrolysis suggested the experimental work undertaken for the purpose of developing an accelerated test for the efficiency of paint used on metallic surfaces. When iron is coated with a protective paint, no corrosion takes place as long as moisture and air can be excluded. Whatever the real mechanism of corrosion may be, it is recognized that a paint must protect the metal surface by insulating or excluding it from the activity of air and moisture. Any means, therefore, that may show the resistance of paint materials to the breaking down of the coating film may be used to measure the comparative value of such films with regard t o their permanency or endurance under actual and less active conditions. The apparatus used in obtaining the data given in the tables below consists of a simple electrolytic cell containing a normal salt solution for the electrolyte. The anode was a piece of clean steel coated with the paint t o be tested. The cathode was platinum and the electrodes wei-e placed four inches apart. Eight volts of direct current were used. A milliammeter was connected in the circuit to indicate the current flowing. Ammeter readings were taken as shown in Table I11 and from these readings and the constant voltage, the wattage was computed. The painted electrodes used were made of pieces of steel about 1.4” long, 1.0’’ wide by 0.3” thick. A piece of copper wire about six inches long was fixed into one end of this steel rectangle b y first cutting across the end with a hack saw a notch about an eighth of an inch deep and then wedging the wire into it. The diameter of the wire should be a little greater than the width of the saw kerf. The wire was then bent upwards as shown in the accompanying sketch. The electrodes thus made were given two coats of paint, about a week being allowed for the first coat t o dry. When the second coat was apparently dry, the electrodes were placed in an oven and kept a t 4;’ C. for 1 2 hours. I n order to facilitate rapid and uniform drying, it was found advantageous to round the edges Qf the electrode. (All the tests given in Table I11 except red lead ( a ) and aniline pitch dip were made with square cornered electrodes.) The electrodes were all of the same area and immersed in the solution t o the same depth. The results are given in Table 111. For the purpose of this experiment, the insulating efficiency of the paints tested is taken as inversely
Sept., 1911
I
proportional to the wattage a t the end of six hours. With a constant voltage, the efficiency is also inversely proportional to the average conductivity for the first six hours. While in general the experiments were conducted for 24 hours, in some cases the paints broke
E/ectrode. NfffUrQ/ SCP/e
Skmh
down so completely before that time that the test was discontinued. For this and the additional reason that, in most cases, a nearly constant current had been reached b y the end of six hours, t h a t period was made the basis of comparison.
T H E JOURA’AL O F I N D U S T R I A L A N D ENGIA’EERIXG C H E M I S T R Y .
Sept., 1911
ABLE LE I --PASSIVITY.
BCBBLIKG TEST.
ProXI-eight. portional Steel Lost. k e a of steel. Pigment or base of Gram. 0.938 1 Aluminum paint. . . . 0 . 0 5 6 2 0.939 2 T a r cement paint. . . 0.0780 1.000 3 -1sphaltum paint. . . . 0.1000 0.921 4 Red l e a d , , . . . . . . . . . 0.1390 1.032 5 , Pitch p a i n t . , . . . . . . . 0 , 2 0 3 0.912 6 . Acheson graphite. . . . 0 ,222 1.000 7 , R . I. \V.paint. . . . . . 0 279 0.912 8. P. Sr B. p a i n t . . . . . . . 0.298 0.982 9. Slate lacqiier.. . . . . . . 0 . 3 5 5 0.904 LO. Cement paint. . . . . . . 0.4441 ’rAELI: JI.-p.ASSIVITY.
XVt lost per unit ax ea. 0.0598 0.0832
Relative inhibitive value.
0.:000
0.59s
O.l.510 0.i970 0 . ? 160 0.:!790 0 32iO 0 ,2650 0.491
0.396 0.302 0.277 0.214 0.155 0,16? 0.122
other of an insulation type like the one above described, are necessary to determine the efficiency of a paint. By carefully standardizing these tests it should be possible to compute the value of a paint in relation to some commonly accepted unit. By way of illustration, we may use red lead for one example and aniline pitch paint for the other. The problem is t o ascertain the relative efficiency of these two paints. Let “ I ” equal the inhibitive value of a paint and “ R ” the resistant or insulating value of the same paint, then “ V ” the total value of the paint equals “ R I . ” (An absolute standard to which to refer the inhibitive and insulating values of a paint must, of course, be eventually chosen.) In the case of red lead T’ = 0 . 2 8 2 X 0 , 3 9 6 = 0 . 1 1 2
1.000 0.71s
DAJIPFILXTEST, Pigment o r residue.
Order of efficiency
67 I
1 . . . . . . . . . . . . . . . . . . . . . . . . . Red lead P . S: B.paint Aluminum paint 3........................ Asphaltum paint 4. . . . . . . . . . . . . . . . . . . . . . . . T a r and cement paint 3. . . . . . . . . . . . . . . . . . . . . -4cheson graphite 6............. , . . . . . . . . . . . . . . . . . . . . . . . Slate lacquer
and for aniline pitch paint T’
0,473
x
0.302
= O.Ii+j,
TABLEIII.-INSULATIOS TESTS.
. *(
-
ti of coats.
pio.
Paint used.
2 1 R I . \\’. p a i n t . . .... 2 2. Pitchliianiline . . . . . . . . 2 3 Red lead (a).. . . . . 4. Red lead ( b ) . . . . . . 2 5 . Cementpaint . . . . . . . . . . 3 6 . Acheson’s graphite. . . . . 2 7 , P . & B. p a i n t . . . . . . 2 8. l s p h a l t u m paint. . 2 . 2 9. Whiteshellac . . . . . . . . . . 10. Slate lacquer.. . . 2 11, Aluminum paint. 2 12. Dull black var-lac., . . . . 2 Pitch d i p l . , . . . . . . . . . . . very thick 1
Amperage a t end of
2 -
f
Omin 10niin. 30min. 8 . 0 0.002 8.0 0.002 8 . 0 0.000 8 . 0 0.000
8.0 0.025 8 .O 0 . 0 S 8 . 0 0.020 5 . 0 0.025 8 . 0 0.000
8.0 0 . 0 1 0 8 . 0 0.085 5 . 0 0.120 8 .O 0 . 0 0 2
7
6 hrs. 24hrs. Omin.
0.013
0 . 0 4 0 0.0006
0,0693 0.1466 0.2456 0.3180 0,3756 0,5227 0.751 0.7695 1.1225 1.1569
0.010
0.010 0.015 0.015 0.028 0.054 0.075 0.130 0.120 0.180
..
0.020 0.020
..
..
INTERPRETATION O F RESULTS.
To obtain a comparative rating, the efficiency of some one paint was taken a t unity and all others calculated on t h a t basis. It is the opinion of the writers t h a t two accelerated tests, one of the inhibitive character described b y Cushmans and the
BfL
24 hrs.
1.00 . 0,473 0,282 0,218 0.185 0.131j . . 0.0923 o.ogoo . . 0,0615 4.8019 0 . 0 6 0 0,5273 0,8666 2.095 2.168 1.545 2.323
..
.. ..
. I
..
..
0,0130 0.0130
Efficiency = K/\V6. Assuming efficiency of R . I. IT-. = 1 . Wattage a t end of 6 hrs. = \Ve.
described b y Cushman.1 Table I gives numerical values from the bubbling test while Table I1 gives the relative efficiency of the paints as determined by the damp film test. A number of the paints were tested b y Magnussonx a n d Smith,’ in attempting t o find means t o prevent the corrosion of iron in concrete. While in these experiments, the conditions were different, the results in the main tend to confirm the same order of relative efficiency.
Bull. 35, Office of Public Roads, U. S. Department of Apriculture. A . I . E.E. Proceedings, 30, 939 (May, 1911).
0.012 0.040 0.090 0.045 0 . 0 9 0 0.065 0 . 0 7 0 0.088 0.100 0.130 0.130 0.130 0.140 0.200 0 . 2 0 0 0 . 2 1 0 0.210
30 min.
I hr.
0.0028 0.0073 0.0193 0.040 0.0006 0.0031 0.0091 0 . 0 2 6 6 0.005 0.115 0.00025 0.0021 0.0081 0 . 0 2 5 6 0.010 0 . 1 1 5 0.0002 0.0024 0 . 0 1 1 5 0.0450 0.042 0 . 0 6 0 0 . 0 0 4 5 0.0171 0.0411 0.1056 0.066 0.100 0.0094 0.0300 0.0652 0.1467 .. . . . 0.005 .. 0 . 1 0 1 0.231 0.15 . . . 0.0104 0.0463 0.1045 0.2295 0 . 1 0 0 0.150 . . . 0.00 0.0500 0.1325 0,3225 0 . 1 2 0 0.155 0 . 1 8 0 0.195 0.0126 0 . 0 5 5 4 0.1419 0.3369 . . . . . . . . 0.0183 0.0749 . . 0.155 0.185 .. 0 . 1 5 0 0.150 . . . . . . . . 0.0225 0.0773 . . .. 0.0025 0.0025 0.0020 0.0010 0.000 0 . 0 0 0 0.0002 0 . 0 0 5 5 0.0095 0,0110
0.008
I n order t o obtain other means for comparison, the same paints were tested by the accelerated tests
Cif.
2 hrs.
6 hrs.
.\lot comparable with others.
a LOG.
--7
2 hrs.
0.005 0.005 0.003 0.003 0.032 0.058 0.100 0.106
1 hr.
COMPARISON T E S T S .
2
..0 3
K a t t a g e a t end of
? -----_----
-.
8
j
.33
Then K = 0.0693.
comparative results which are consistent with service tests of a limited character. LABORATORY OF IXDUSTRIAL CHEMISTRS, UNIVERSITYOF WASHINGTOK.
-_____ A THERMOSTAT FOR MODERATE TEMPERATURES. B y -4. 11. BUSWELLAND RALPHH. ~ I c K E E . Received August 7, 191 1.
The ordinary thermoregulator consisting of a mercury interrupter and relay, operated a t low voltage, for turning on and off the heating system (electricity or gas), has given satisfaction. The other simpler type of thermoregulator, depending on the effect of temperature on a gas or a liquid, placed in a vessel whose only outlet is a J shaped tube filled with mercury and having platinum wires piercing each arm t o serve as binding posts for the electrical connections, is, in the forms previously used,I for a short time fairly satisfactory where a range of several degrees is allowable. But when it is desired t o keep a n in-
’
Summerville, Elec. W o r l d , 57, 112 (1911); cf. bibliography given by Geer, J . Phrs. Cizem.. 6, 101 (1902).
