ISDUSTRIAL A S D ENGINEERING CHEMISTRY
910
still has a considerably higher osmotic pressure than does the white. Bialaszewiez also found that the osmotic pressure of the yolk decreased during the first few days of incubation. He explains this decrease as due to the passage of water from the white to the yolk. Rice and Young (4) determined the freezing-point depression of the yolks and whites of eggs from five different breeds and found no significant differences bctween breeds in this respect. The average freezing-point depression for the yolks was 0.587' C. and for the whites, 0.437' C.
51 I
53k
-
2460
I- 45.
\
3T0C 98.6'F.
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Figure 4-Progressive Decrease in Total Solids of Yolks as Eggs Are Stored for Increasing L e n g t h s of T i m e a t Various Temperatures
The accepted commercial range in temperature for the storage of hens' eggs is from 29' to 31" F. (-1.7' to -0.6" C.), although in some instances it may be slightly lower. This is about 6" F. (3.3' C.) below the minimum observation temperature recorded in the experiments reported in this paper. I n this connection i t may be of interest to call attention to the fact that eggs may be stored for months at temperatures which are approximately 1 " C. below their actual freezing point. This is a case in which commercial advantage is taken of supercooling to permit the preservation of a food product at a lower temperature. The average total-solids content of the yolk of fresh eggs fluctuates around 52 per cent, as given by various workers and according to our own figures. The determinations should be made within 2 to 4 hours after the eggs are laid; failure to make the solids determinations s3on enough may account for variations in some published data. Willard and Shaw ( 6 ) .in a study of a large number of individual eggs from differ-
VOl. 22, No. 8
ent breeds, gave 51.37 per cent as a grand average for the total solids in the yolk. Pennington, Jenkins, St. John, and Hicks (3) gave 52.56, 52.04, and 52.46 per cent as the average values for three lots of fresh eggs which they examined. Water may pass into the yolk until the solids content drops to 44 per cent as representing some of the lowest values which we have found. Ordinarily the yolks tend to break when t'he egg is opened if the solids content of the yolk has dropped to the neighborhood of 46 to 47 per cent. Calculations indicate that the average yolk may increase in size by about 11 to 18 per cent, as a result of the entrance of water. The total-solids content of the yolks was determined for the eggs used in the experiment described in connection with Figure 3. Figure 4 presents the change in total solids of the yolk when the eggs are held a t various temperatures for increasinglengths of time. It will be observed that as the temperature of storage is increased the rate of passage of water into the yolk is also increased. The general effects of temperature as represented in Figures 3 and 4 are quite similar. The variation in the total-solids content of the yolks of the different eggs introduces a slightly greater experimental error than does the measurement of the standing-up qualit'y of the yolk. The flattening of the yolk is undoubtedly influenced by the decrease in viscosity due to the passage of water into the yolk. The decrease in the viscosity of the yolk content', because it flows more readily, causes the yolk to assume a flattened shape. The passage of water into the yolk must increase the size of the yolk and consequently stretch and weaken the yolk membrane. Furthermore, the membrane mustj be larger to surround the flattened yolk than the spherical one. These changes finally proceed so far that t'he egg cannot be broken into a dish without the yolk breaking. The passage of water from the white into the yolk can be retarded by evaporation of water from the white to the air, thus bringing the two parts of the egg more nearly into wat'er equilibrium. Actually, of course, this exchange can be reversed by evaporating enough water from the egg so that the yolk will give up water to the white, in which case the yolk increases in total solids. As long as much emphasis in the grading of eggs by candling is placed on the size of the air cell, the prevention of the weakening of the yolk by evaporating water to the air is undesirable. Literature Cited (1) Bialaszewiez, Arch. Enlwicktungsmech. Organ., 34, 489 (1912). (2) Greenlee, U. S. Dept. Agr., Bur. Chem., Circ. 83 (1911). p) Pennington, Jenkins, St. John, and Hlcks, U. S. Dept. Agr., Bull. 5 1 (1914). (4) Rice and Young, Poicltry Sci., 1, 116 (192s). (5) Sharp, Science, 69, 278 (1929). (8) Willard and Shaw, Kansas 4gr. Expt. S:L., B!cIl. 1 5 ) (1333).
Detinning of Scrap Tin Plate' Wilfred W. Scott and Ne!e E. Davis UNIVERSITY OF SOUTHERN CALIFORNIA. Los ANGELES,CALIF.
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HE recovery of tin from old cans and other tin-plate materials has been attempted by many methods, most of which have been unsuccessful. The few successful detinning plants have employed the chlorine, alkali, or electrolytic alkali process. I n the past two years most of the detinning plants in operation have been closed because of the low price of tin. The present writers have investigated a new detinning 1 Rectived
December 9, 1929.
process which is based on the fact that dilute solutions of tartaric acid dissolve tin in the presence of an excess of air or oxygen while iron is unattacked. It is common knowledge that fruit acids dissolve tin, but a review of technical and patent literature has revealed no case in which this fact has been utilized in the removal of tin from old tin cans. When tin-plate scrap is placed in dilute tartaric acid solution, tin is dissolved a t the surface of the solution. I n order t o effect a more rapid sdution of tin, it was found ne2essary t o provide
August, 1930
I.!’DCSTRIAL AND ENGINEERIiVG CHEMISTRY
a more efficient method for the uniform contact of air and acid on the tin-plate material being detinned. Attempts were made to detin the scrap by spraying with dilute tartaric acid solution. The tin was dissolved a t a fairly rapid rate, but the method was considered unsuccessful because considerable solution was lost by dispersion of the solution into the atmosphere. A more efficient method for detinning was perfected in which the scrap was placed in a cylinder,. partially submerged in dilute tartaric acid solution. A detinmng apparatus consisting of a perforated steel cylinder 6 inches in length and 33/4 inches in diameter and a detinning tank 71/* inches in length and 5 inches in width was constructed. The cylinder, containing the tin-plate scrap, was turned on a 1/4-incli steel shaft which passed through the length of the cylinder and detinning tank. I n the process of detinning the solution level is regulated to cover about one-third the cross-sectional area of the cylinder. The scrap contained in the cylinder is thus subjected to the alternate action of acid and air. Three hours was found the most efficient length of time to conduct detinning and the acid was most effective a t 5 per cent concentration. The solution after detinning, contains stannous tartrate. The tin may be recovered from the polution by precipitation
911
as sulfide with hydrogen sulfide. The tin from stannous tartrate is replaced by the hydrogen from hydrogen sulfide and tartaric acid is recovered. There is a slight loss of tartaric acid in this reaction owing t o decomposition, which is about 0.10 gram of acid per gram of tin recovered. The tin sulfide may be converted into the chloride by treating with hydrochloric acid. The detinned scrap contains about 0.10 per cent tin, which is sufficiently low to be suitable for steel smeltering. In the detinning of old tin cans it would be necessary to clean the cans first with hot sodium hydroxide or carbonate ( 1 ) . The presence of grease and lacquers will inhihit the action of tartaric acid on tin. The cost of detinning tin-plate materials by the method outlined above, since it has been attempted only on a laboratory scale, cannot be accurately estimated. The equipment necessary to conduct detinning with tartaric acid method is simpler than that required in the chlorine and alkali processes and would be less expensive. The cost of acid consumed, as determined in our investigation, is 3.7 cents per pound of tin recovered. Literature Cited (1) Butterfield, U S Patent 1,511,590 (December 15, 192&).
Properties of Shellac Films I-Resistance of Shellac Films from Various Varnishes to Action of Water and Chemicals‘ M . Venugopalan and M. Rangaswami INDIAN LAC RESEARCH IXSTITUTE. NAMIUMP. O . , RAXCHI,B . hT,R Y . , IXDIA
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‘ITH the view of stabilizing the use of shellac in the varnish industry, the action of different solvents for making shellac varnish was investigated. (Bulletin No. 1, Indian Lac Association for Research, 1928) The effect of common alcohols, such as methylated spirit and wood naphtha, on the viscosity and solvent power of the solution has already been reported ( 1 ) . It was found that wood naphtha exhibited the peculiarity of combining the two essential properties of a varnish solvent, high solvent power and low viscosity, at a particular concentration, and this was considered to Le due to the complex nature of this solvent. This work was followed by a study of the effect of binary mixtures of some common solvents with reference to these two properties ( 2 ) . Three types of mixed solvents of varying proportions were tested-i. e.. alcohols and alcohols, alcohols and esters, and alcohols and ketones-and from a study of these two properties it was possible to compare the efficiency of the different mixtures in terms of the ratio of the solvent power number to the relative times of flow. I t was found from these figures that, except in the case of alcohols and esters, a mixture of two solvents always shomed a higher efficiency than either solvent taken singly, and a mixture was found in most cases which showed the maximum efficiency. Furthermore, in the case of ethyl alcohol-ethyl acetate mixture and more particularly of mixtures of alcohols and acetone, the mixed solvent proi-ed to be more efficient than the pure alcohol, though the mixture contained a nonsolvent for shellac. I n view of the lorn price of acetone compared with that of alcohol, the economic advantage of employing the optimum mixture of the two in preference to the pure alcohol was indicated. 1
Received April 29. 1330.
It was, however, considered essential to examine the quality of the films obtained from these mixtures, and in this paper the resistance of the films from various solutions to the action of water and such chemical agents as acids and alkalies has been discussed. I n these tests only those mixtures have been used which proved to be the optimum mixture of two solvents in the prerious work, together with the three alcohols for comparison. Preparation of Varnish Films The varnish was prepared by dissolving 50 grams of specially made “Lvax-free” shellac in 100 cc. of the solvent in the cold with the aid of shaking Films were prepared on glass slides by pipetting 2 cc. of the varnish onto the center of the slide and spinning the latter on a turntable at 300 r. p. m. The films were then dried for a week before testing. Owing to the different viscosities and densities of the various varnishes, different film thicknesses were obtained, but as the object was t o study the behavior of the different solvents under identical conditions, no attempt was made to get identical thicknesses by varying the speed and duration of spinning. Only in two cases, however, were extremely thin films obtained (Table I). Table I-Thickness
of F i l m s from Various Yarnishes MEANFILM
SOLVE\T COYPOSITIOh
Methyl alcohol Ethyl alcohol Propyl alcohol Methyl alcohol-ethyl alcohol, 1 . 1 Methyl alcohol-propyl alcohol, 3 : 1 Ethyl alcohol-ethyl acetate, 3 . 2 Methyl alcohol-acetone, 3 : 2 Ethyl alcohol-acetone, 2 3 Ethyl alcohol-ethylmethyl ketone, 1 : 3
THICKNESS Mwons 46 50 20 50 50 21
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