I20
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
used on automobiles, in order t o make comparisons with solvents in industrial use as t o the amount of gas absorbed, the candle power of the light given on burning the gas from the tank, the loss of solvent, etc. The other solvents were c . P. acetone and a complex mixture of organic liquids, which is used as a solvent for acetylene, and which will be referred to in the accompanying curves as ester-ketone-aldehyde solvent since it undoubtedly owes its absorbent power to the presence of bodies belonging .to these three groups. Probably the most important point of comparison is brought out in the curve for each solvent where the candle power at various times of the discharge is shown; a striking difference between the volatile and the non-volatile solvents appears here. With the non-volatile solvents there is little more than an hour’s warning before the gas is gone completely, while with the volatile acetaldehyde solvent there is an interval of from four to six hours in length from the first warning and the “going out” of the light. With the acetaldehyde, there is a round black spot in the flame that makes its appearance at about the 35 candle power point of the curve, and the size of this spot increases as the candle‘power drops, its appearance giving about six hours warning, where two cu. f t . burners are being used. The loss of solvent, which runs in common practice with the nonvolatile solvents from 4 t o 6 ounces for each discharge of the tank, was a fraction over 12 ounces in the acetaldehyde experiment, where the evolution of the gas was pushed to the limit, and would undoubtedly run about 8 ounces in industrial use. At first glance it appears rather surprising that the drop in candle power with the increase of solvent vapor in the gas is not greater. For example, it is seen from the curve where candle power is plotted against per cent. of solvent vapor in the gas, that when the solvent vapor has increased to 80 per cent. the candle power is still above 2 0 . I t has been noted by other observers that diluents lower the candle power of acetylene more rapidly, the lower the flame temperature of the diluent. Since acetylene has a heat of 313.8 cals. per gram molecule, and acetaldehyde has 279.2, we have a satisfactory Of the action of the diluent in this case; the calculated temperature Of the hottest part Of the oxy-acetylene flame is in the neighborhood Of 4 0 0 0 ~c. and that Of the OXYacetaldehyde flame is above 3400’ C. The aldehyde vapor is a good diluent aIS0 for the reason that the volume of air or of oxygen required for its combustion is theoretically exactly the same as that required for acetylene, so that there is scarcely any change in the shape of the flame, as the:Percentage of aldehyde vapor increases. These two facts, the high heat of combustion and the Of the Of air Or Of oxygen needed, make for an advantage in the use of acetaldehyde as a solvent for acetylene to be used in welding and cutting operations. I n an emergency repair job in a remote locality, in case the gas gives out, the work can be finished by drawing On the for the combustible.
Feb., 1913
Long observation has shown that the figures attained in industrial practice with the non-volatile solvents noted above, average 37 ounces acetylene in 8 5 ounces solvent, at a temperature of 70’ F. and a pressure of 250 pounds gauge. I n this experiment with acetaldehyde as the solvent, 48 ounces of acetylene were absorbed in 82 ounces of solvent, with the gauge standing a t 265 when the temperature rose to 70’ F. This figure shows that acetaldehyde is a liquid that has a superior absorbent power for acetylene ; in fact, the author ventures the statement that this experiment shows an amount of acetylene greater than has ever before been stored in a given volume of solvent. CONCLUSIONS
I. Acetaldehyde fulfils the industrial requirements for an acetylene solvent. 11. The volatility of acetaldehyde can actually be turned t o advantage. 111. Since acetaldehyde can be made in one chemical operation directly from denatured alcohol, we have here a source of supply of an acetylene solvent which will not increase in price, but which will undoubtedly become cheaper as improved methods of agriculture make it possible to produce denatured alcohol cheaper. Acknowledgment.-I am indebted to my former student assistants, Messrs. E. P. Poste and E. W. Gardner, for their help in taking readings and making records in the above experiments. I wish also to express my thanks to Dr. H. S. Hower, of the Physics Department, Carnegie Institute of Technology, for assistance in taking the candle power readings and for the loan and standardization of the Brodhun Portable Photometer, which was used in the photometric part of the work. CHEMICAL DEPARTMENT OF TECHNOLOGY CARNEGIE IXSMTUTE
PXT-TSBURG t
TESTS ON THE OPACITY AND HIDING POWER OF PIGMENTS‘ By G. W. THOMPSON
I n the discussion of paint problems, certain terms are often used with such different meanings that great confusion has resulted. Thus, the word ing power ” is defined in three or more different Senses by D ~ ~. ~ in his d articles l in~ the 8~e ~ a i l r o a dand Engineering Journal” running in the issues of 1890 and the word b,. c = incident light unity. x = proportion of incident light reflected which is independent of the thickness of the film except for very thin films. a Then -2 = proportion of entering light transmitted by =
-
-
a,
b, - b, thickness of paint, a, being the light entering the b, - b, film as it is the light transmitted by the b, film. It is necessary that we give here the development of a formula for the light that passes through any number of units of thickness of paint. L = the light passing through any number of thickness units. S = the light absorbed by any thickness unit or units. a the light striking the first surface. L A = the ratio -
-
U
S
-U
B
=
1z
= the number of units of thickness.
P
=
the ratio
= I
-A.
the constant opacity of each unit of thickness in the form of a decimal fraction of unity. Light passing through no unit of thickness: = a LO = a Light passing through one unit of thickness: L, = a-Pa = a(1-P) Light passing through two units of thickness: L, = (a-Pa)-(a-Pa)P = a(1-P)' Light passing through three units of thickness :
L,
=
L,
=
{(a-Pa)-(a-Pa)P~-
{ ( a- Pa - ( a-P a ) P 1 P = a( I -P)S a(1 -P)" n -
=
An General formula . A, = ( I - P)" B,=I --A,= I - ( I -P)" From the formula A, = ( I -P)", where A, is the U
a .
proportion of entering light transmitted, P is the opacity of unit thickness in terms of decimal of unity and n is the number of units of thickness.
From formula B, = I - ( I -P)" where B, is the proportion of entering light absorbed:
T H E JOURA’AL OF I-VDb-iSTRIAL A N D E-VGINEERIATG C H E M I S T R Y
Feb., 1913
I
-x
= proportionpf
Bb
(I-%)
incident light entering b, film. X+CZ, = c = I
+
the different white pigments, tested on the formula given above, are shown. The values for P are the coefficients of opacity as defined above. The reflection is the proportion of incident light reflected and is expressed in decimals of unity. Pigment.
x fa,
123
Coefficient of opacity P
White lead-Dutch.. . . . . . . . . . . . . . White zinc--American process.. . . . White zinc-French Pr. . . . . . . . . . . Lithopone.. . . . . . . . . . . . . . . . . . . . . . Calcium carbonate. . . . . . . . . . . . . . . Basic lead sulphate.. . . . . . . . . . China clay. . . . . . . . . . . . . . . . . . . . . . Asbestine. . . . . . . . . . . . . . . . . . . . . . . Calcium sulphate.. . . . . . . . . . . . . . . . Silica., . . . . . . . . . . . . . . . . . . . . . . . . . Barytes.. . . . . . . . . . . . . . . . . . . . . . . .
-1
from which
Reflection’ 0.935 0.956 0.964 0.947 0.969 0.927
0.0671 0.0794 0.0645 0,0578 0.0136 0.0813 0.0190 0.0090 0.0030 0.0102 0.0114
0,823
0.859 0.856 0.793
0.856
This work was done in the research laboratory of the National Lead Co., much of it having been accomplished with the assistance of one of my associates, Mr. R. L. Hallett, to whom I tender thanks.
This formula looks rather complicated, but, in practice, and by the use of logarithmic tables, the work is more simple than it seems on first inspection. The apparatus to which I refer reads to the one tenthousandth of an inch and, preferably, should have been constructed with the millimeter scale. It is a simple matter, however, to make conversions into the mm. scale. In making these calculations, it is to be observed that, the comparison of the pigments having been made between glass surfaces, the amount of light reflected from the adjacent surfaces of a paint would probably be different from the light reflected from the surface of paint which is adjacent to air. This is a controlling reason why the reflected light should not be considered in calculating the coefficient of opacity. In testing pigments for their coefficients of opacity, we have followed the plan of mixing these pigments with linseed oil on a standard formula of 2 5 per cent. by real volume of pigment and 75 per cent. by volume of oil. In some cases, as, for instance, in the case of zinc oxide, this may be too large a volume of pigment, to handle conveniently in the apparatus; but, if trouble is experienced, a different formula can be used, comparing i t with another standard pigment on this changed formula. This apparatus is somewhat new and me have not as many results to report of work done upon it as could be desired, and what we present here is simply for information; and, so that the subject may be more generally studied, we present here some determinations made in this apparatus, working on a number of white pigments. I t is not to be supposed that these tests represent average pigments or that thc results presented are for the purpose of condemning any of the pigments tested. It is very probable that the pigments upon the market, of the kind described, vary considerably from the figures presented here. The coefficients of opacity and the light reflected by
AN APPLICATION OF THE ELECTRIC RESISTANCE FURNACE TO THE DETERMINATION OF OXYGEN IN IRON AND STEEL B y R . H. MCMILLEN Received January 6, 1913
’
The fact that iron and steel always contain more or less oxygen has long been known, and about thirty years ago, Ledeburr called attention to i t and gave a method for its determination. I t is only recently, however, that the requirements in the manufacture of high-grade steels have become so exacting that the determination of oxygen in steel and other materials has come to be one of the routine determinations required of a steel laboratory. The Ledebur method, which is well known, consists in heating the sample of iron or steel in nitrogen to remove all moisture without oxidizing i t , then reducing the oxides a t a red heat by hydrogen and absorbing and weighing the resultant water. Cushmanl has shown that the drying of the sample in nitrogen is unnecessary, his results being but slightly higher than those by the original method. When used with electric resistance furnaces, this method is very satisfactory for the determination of oxygen in iron and steel, tungsten,~and other non-volatile metals. Even this method, however, will fail to show all the oxygen in metals containing oxides of silicon, vanadium, titanium, and other elements whose oxides are not reduced below 950’ C.4 The following modification of the Ledebur method has been found to give most satisfactory results: APPARATUS
The apparatus consists of two electric resistance Sauerstoffbestimmung im schmiedbaren Eisen, Stahl u.Eisez, 2, 193. “The Determination of Oxygen in Iron and Steel,” THISJOURNAL, ‘3, 372. 3 Tungsten powder often contains a rather large percentage of oxides. Some commercial samples investigated by the writer recently have shown an oxygen content corresponding t o 12 per cent. WOa. I t is probable, however, that the whole of the oxygen is not combined with the tungsten. 4 See “The Determination of Oxygen in Iron and Steel, b y Reduction in an Electric Vacuum Furnace.” by W. H. Walker and W. A . Patrick, THISJOURNAL, 4, 799. 1
