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
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relatives. T h e ferrous silicates are green, t h e ferric, yellow. Copper glasses, when t h e batch contains a n oxidizing agent, are blue a n d here again t h e color is t h e same as t h a t imparted t o a dilute aqueous solution b y t h e cupric ion. T h e color imparted t o glass by cobalt oxide is practically identical with t h a t produced by a n excess of concentrated HC1 in aqueous CoClz solution where t h e complex CoC14 is supposed t o form. The color of vitreous manganese solutions resembles t h a t of aqueous solutions. Similarity in valence was recently shown by Scholesl in his article on “Trivalent Manganese in Glass.’’ In opal and alabaster glasses we encounter another striking parallel t o conditions in aqueous solutions. Opalescence is largely due t o finely divided alumina of colloidal size. Just as electrolytes will precipitate such colloids from aqueous solutions, so NaCl or NazSOl or other chlorides or sulfates will precipitate this colloid from vitreous solution. As a result, a glass which is opalescent without t h e addition of one of these salts becomes a n alabaster glass if t h e y are added, through t h e precipitation of t h e colloid b y t h e salt. The light t h e n transmitted is white. When t h e sulfate ion is present t h e color is more intense t h a n with t h e chloride ion. Effects resembling t h e Liesegang layers have been obtained in opal glasses t o which COO a n d selenium were added. T h e alternating s t r a t a are blue a n d white when t h e glass gathered from t h e pot is allowed t o cool without reheating. CONCLUSION
The d a t a presented seem t o indicate clearly t h a t much might be accomplished b y studying vitreous solutions, in part a t least, on t h e basis of similar phenomena observed in aqueous solutions of some of their constituents. T h e writer hopes t o a d d evidence through researches which are under way and planned. SCHOOL OF CHEMISTRY UNIVERSITY O F PITTSBURGH PITTSBURGH
CHEMICAL COMPOSITION vs. ELECTRICAL CONDUCTIVITY2 By COLING.FINK
Some years ago, while still a t t h e university, I carried out a number of experiments on t h e electrothermic production of ultramarine. Powdered mixtures of sodium sulfide, china clay a n d carbon were interposed between carbon electrodes in a closed crucible furnace. I observed a t t h e time t h a t in order t o keep t h e electrical resistance a n d t h e temperature of t h e charge fairly low so as t o avoid decomposition of t h e ultramarine as soon as i t was formed, i t was necessary t o use very finely divided carbon, such as lampblack. With charges made u p of powdered coke which was coarse compared t o t h e lampblack, I could THISJOURNAL, 7 (1915), 1037. Presented at the 53rd Meeting of the American Chemical Society, New York City, September 25 to 30, 1916. 1
2
Vol. 9, No.
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not get a n y appreciable current t o pass between t h e carbon electrodes u p t o potentials of 2 jo volts. Subsequently, I have found repeatedly t h a t t h e electrical conductivity of mixtures of finely divided substances is a function of t h e relative size of t h e components. E X P E RI h.1 E NT A L
A series of tests was made in order t o get values of a more quantitative nature. Two substances were selected, t h e physical properties of the one as divergent as possible from those of t h e other: a black metal powder, tungsten, and a white insulator powder, thoria. The advantages in this selection are manifold; both tungsten and thoria will stand very high temperatures and can therefore be made practically moisture-proof. I t is a well known fact t h a t in all high-resistance tests adsorbed moisture is a very disturbing factor. Metals such as copper and silver were not serviceable since they cannot be heated to high temperatures without partial -qaporization, which though slight was sufficient to cover the surface of t h e insulator granules with a highly conductive film. Other factors that decided our selection in favor of tungsten a n d thoria were: ( r ) high state of purity; ( 2 ) availability of both in extremely fine powdered form (readily sifted through 2 j o mesh gauze); (3) constancy and stability under ordinary atmospheric conditions; (4) sharp distinction in color; ( 5 ) high specific gravities (which reduced t h e tendency t o dust). All mixtures here recorded were made up of equal weights of tungsten a n d thoria. As regards t h e size of the particles, as stated above, t h e mixtures would pass readily through silk having 2 5 0 meshes t o t h e inch. The holes in this silk are about 0.001 in. in diameter. All attempts t o segregate particles of a well-defined size by such methods as suspending water, organic liquids or air, were frustrated o n account of t h e persistent tendency of t h e very fine particles t o form agglomerates. We finally resorted t o t h e familiar “ t a p test.” This gave us fairly good comparative values of t h e fineness of t h e various powders used. T e n grams of t h e powder or powder mixture were filled into a I O cc. glass graduate a n d tapped t o constant volume; usually, after 7 minutes no further decrease in volume could be detected. The ultimate volume in cc. divided by I O gave us t h e relative volume (vr) as recorded in Table I. It can easily be demonstrated t h a t t h e values for a, are a function of t h e density a n d mean particle size. At first there seemed t o .be a serious objection t o t h e t a p test, namely this, t h a t a powder composed of, say, equal parts of coarse and fine particles would give t h e same figure for vr as a second powder whose particle size was a mean between t h e two limiting sizes of t h e first powder. This objection t o t h e t a p test was automatically set aside since in t h e ordinary preparation of metal or oxide powders in single small lots b y far t h e greater majority of particles are approximately of t h e same size. This tendency t o f o r m a ‘Lstandard”size is a universal phenomenon, t h e dimensions of a n y particular standard
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
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being dependent upon t h e physical factors such as temperature, strength of solution, etc., under which t h e particular powder is prepared. (Compare also, t h e size of t h e crystals of granulated sugar and t h e “Strike pan.”) TABLE I
-RELATIVE Mixture
ThOz
R . . . . . . . . . . . 0.720
P . . . . . . . . . . . . 0.720 2. . . . . . . . . . . . 0.676
VOLUME
(f’,)
OP-
MIXTURE Found Calc.
m
0.430 0.565 0.389 0.200 0.275 0.420
0.113 0.350 0.238 0.113 0.330 0,577
0.417 0.535 0.406 0,209 0.31h 0.40h
Appearance of Mixture White White White White Black Black
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Our results tend to show t h a t under ideal conditions of mixture relative grain size, uniform distribution, etc., t h e resistivity values for white mixtures such as 2 would be even higher t h a n here recorded. Similarly, t h e resistivity xralues for black mixtures such as X would be lower t h a n those found, approaching a limiting value equal to twice t h a t of t h e IOO per cent metal rod. CO~CLUSION
I n general vie may say t h a t t h e electrical conductivity s. . . . . . . . . . . . 0 . 3 0 5 of a substance is primarily dependent upon t h e shape x . . . . . . . . . . . 0.238 a n d t h e distribution of t h e fundamental grains or Referring t o Table I , we note t h a t t h e thoria pow- particles composing t h e substance, a n d secondly, ders varied i n relative fineness between 0 . 7 2 0 a n d 0.238 upon t h e presence or absence of thin films of secondary and t h e tungsten powders between 0.577 a n d 0.113. material enveloping these ultimate grains. The calculated value for ’J, of a n y mixture is equal t o On t h e basis of this theory r e can account for t h e one-half t h e s u m of t h e v y values of t h e Tho2 a n d W comparatively high conductivity of gels t h a t contain constituents. These calculated values agree fairly b u t a trace of conducting material. We can also well with t h e experimental and support our con- account for t h e marked difference in resistance of say tention t h a t t h e particles of a n y freshly prepared two samples of commercial copper whose chemical powder are of fairly uniform size. If this were not composition is identical, depending upon whether t h e t h e case no such agreement between t h e calculated impurity, such as sulfur, is uniformly dissolved in the a n d experimental values would be possible. metal or whether i t forms a film (“cement”) of copper As t o t h e appearance of t h e mixture, if the z’, \ d u e sulfide around pure granules of copper. The latter for t h e white powder is high as compared with t h e case is t o be regarded, as Rancroft suggested, as a n value for t h e black powder? t h e appearance of t h e mix- emulsification of copper in copper sulfide. The high ture is light; if t h e white powder is coarser t h a n t h e resistance of these surface films composed of say sulblack powder, the appearance of t h e mixture is dark. fide or oxide or arsenide accounts €or t h e high reI n other words, whenever t h e ratio of v,. for Tho2 t o sistivity values of copper when but a trace of t h e imvu for W is greater t h a n 2 , t h e mixture is white; if less purity is present. t h a n z t h e mixture is black. [The absolute density of EDISONLAMP WORKS 33 CARLETON STREET W (19.6) divided by t h e absolute density of Tho2 E ORANGE,N E W JERSEY T . . . . . . . . . . . 0,305
(9.8) =
21.
E L E C T RI C A L 31E AS U R E M E K T S
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The powders were pressed into rods 4 cm. lbng and 0 . j cm. square. They were then placed in a tungstenhydrogen furnace and fired a t 1600-16j0~for 3 hrs. This firing caused t h e rods t o sinter together a n d rendered t h e m practically proof against moisture. The fired rods were kept in a P20r desiccator. The rods were t h e n mounted between brass clamps and t h e resistance measured on a Wheatstone bridge with a sensitive galvanometer. Care was taken t o make these measurements on days when t h e humidity of t h e air was 10w.l I n view of t h e differences in “Color” of t h e various mixtures in t h e powdered form, it was not very surprising t o find marked differences in t h e electrical resistances. The firing a t 1600°, hon-ever, resulted in a n almost uniform shade for all of t h e mixtures. I n Table I1 below are recorded four of t h e characteristic resistance values found. I n t h e last column are t h e calculated specific resistance values. Powder ThOn No. 2 Z
X
W No. 1
TABLEI1 Resistance Over 1012 Ohms 41.8 0.0271 0.0040
Resistivity Over 1012 Ohms 173.0 0.108 0.016
The powders, T h o 2 S o . 2 and W KO.I, were pressed up into rods t h e same size as those for t h e mixtures; they were likewise fired a t 1600’ for 3 hrs. 1 Compare in this connection H. Insulators,” P h y s Rev., 3, 490.
L. Curtis, “Surface Leakage over
VARNISH ANALYSIS AND VARNISH CONTROL 11-VISCOSITY OF VARNISHES B y MAXY. SEATON, E. J. PROBECK A K D G. B. SAWYER Received September 25, 1916
The first paper of this series, entitled “Molecular Weights of Vegetable Oils,”’ dealt with a method for determining t h e apparent molecular weights of oil and varnish products, and pointed out t h e value of such a determination. The following paper will, in the same \%yay,deal not only with t h e methods found valuable for determination of t h e viscosity of varnishes, but will also show some of t h e deductions which can be made from t h e study of t h e viscosity determined under varying conditions. Viscosity of such products as petroleum oils has long been recognized as a n important characteristic, and standard viscosities are specified b y most purchasers of such products. Much information has been published, both on t h e viscosity of products of this type a n d on t h e methods available for viscosity determinations, t h e Bureau of Standards and the Bureau of Mines having paid particular attention to t h e subject. Routine determinations of viscosity as a specification constant have also been made on a number of commercial products, among which glue a n d gelatine solutions may be cited. It is only of late years t h a t any considerable attention has been paid to this factor in t h e examination of varnish 1
THIS J o u R s ~ ~ . , 8 (1916). 490
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