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INDUSTRIAL A N D ENGINEERING CHEMISTRY
cigars for packaging by their color into some thirty different grades. This is accomplished mechanically by placing the cigars one by one in position to reflect light from a constant source into a potassium photoelectric cell. The variations in the e. m. f. of this cell control an electrical circuit through a series of vacuum tubes in such a way as to set a combination of pins to drop the cigar into its proper compartment as it passes on in the cycle, according to its accurately determined color. The accuracy and speed with which this machine works would be quite out of the question for a human operator. One hundred and twenty cigars per minute may be readily sorted into thirty color classes by it. Automatic machinery can profitably replace hand labor wherever there is a sufficient number of packages to be made
Vol. 17, N o . 11
and handled. Indeed, the limit below which mechanical operation is less profitable than hand operation is much lower than is commonly suspected and even a few hundred packages a day can be profitably made on machines. Where the production of small packages runs into thousands per day the economies effected by mechanical handling become very great, particularly when uniformity is essential as it is with widely advertised and trademarked articles. Acknowledgment The author's thanks are hereby extended to W. H. Gesell, of Lehn & Fink, and to the American Machine & Foundry Company, through whose kindness the accompanying illustrations are used.
Some Effects of Age on Soap Solutions' By Rosalie M. Cobb RESEARCH LABORATORY OF APPLIEDCHEMISTRY, MASSACHUSETTS INSTITUTE
INCE the aging of soap solutions is an established fact, it would seem advisable to determine the degree to which the phenomenon affects their peculiar properties. In this investigation the effect of age on emulsifying and lathering power was studied.
S
Emulsion Test The apparatus used in the emulsion tests consisted of an ordinary soda stirrer and Counce oil-sampling bottles cut off a t the neck. A stopper was wired to the arm of the stirrer for exclusion of air during the run. As a standard for the emulsifying tendency of the soap solution, the ratio of the equivalents of sodium oleate used in making a 1:1emulsion with Nujol to the equivalents of sodium chloride needed to break the emulsion was taken. This is a modification of the test used by Parsons and Wilson.2 Twenty-five cubic centimeters of Nujol were emulsified by two intermittent stirrings of 30 seconds each, with 10 cc. of N / 3 0 sodium oleate solution; the interval of rest between stirrings was likewise 30 seconds. Water and N / 2 sodium chloride solution were then added in quantities to make the final volume of aqueous phase 25 cc. Upon repetition of the intermittent stirring, if the emulsion separated into two equal layers within 30 seconds after stirring ceased, it was considered broken; if it was not, a fresh emulsion was made up and more sodium chloride and less water were added for the second trial. Thus the only variables were time and rtbsolute salt concentration. Factors Affecting Aging
OF TECHNOLOGY, C A Y B R I D G E ,
MASS
reproduced, the effects of admitting carbon dioxide, oxygen, increasing the temperature, and making up the solution in the presence of three times as much air as before, were determined. The comparative curves are shown in Figure 1. Absolute checks for the maximum and minimum values in Curve 1 were obtained from six N/30 sodium oleate solutions. From these results it was evident that when all factors except the absolute concentration of salt used to break the emulsion were kept constant, the resistance of its emulsions to salting out, and in that sense the emulsifying power of sodium oleate, fluctuated with age. The temperature at which the solutions were aged and the amount of carbon dioxide which came in contact with them had considerable effect on the degree of aging; oxygen had less effect. Lather Tests
In lather tests the usual procedure is to place the soap in "hot" water, degrees unspecified, heat till solution is effected, cool to room temperature, make up to volume, and shake a sample under standard conditions. Under such circumstances it might be expected that the effect of age would be manifest to considerable degree. For the present tests two series of solutions were used. In the first series a solution was made up by the ordinary process as outlined above. The choice of concentrations was narrowed to 0.1-0.2 per cent (dry basis), below 0.1 per cent the small volume of lather allowed too large a percentage of experimental error, while above 0.2 per cent the volume of lather was too large for the tubes and the solutions jelled quickly at room temperature. For the second series It was soon evident that temperature control and exclusion the soap was placed in water a t 85" C., using the same volume of carbon dioxide and oxygen were necessary to secure re- each time, maintained a t that temperature for 20 minutes, producible results. Accordingly, the soap was aged in a cooled to 25" C., and made up to volume. Exposure to air thermostat a t 25" C., withdrawn from its flask through a was minimized during this period, and the pbrtions of solution siphon arrangement fitted with soda-lime and pyrogallol- tested were siphoned off with the usual scrubbers, pyrogallol scrubbers, and made up in boiled distilled water with the and soda lime. In order to get the comparisons on a defisame volume of air present above the solution each time. nite basis, the first tests on both series were made half an Making the solutions up in a flask that had been scrubbed hour from the time the sample was placed in the water. out with nitrogen gave low results which could not be checked, One hundred cubic centimeters of solution were shaken so the attempt was abandoned. one minute in a lathering tube and the volume of lather was When this method yielded results which could be repeatedly read off half a minute later. Curves showing the characteristic difference between the 1 Received July 18, 1925. two series are given in Figure 2 . A 0.2 per cent solution of )THISJOURNAL, 13, 1116 (1921).
INDUSTRIAL A N D ENGINEERING CHEMISTRY
November, 1925
Lux was used. There was no regularity in the behavior of different solutions, In many cases the conditions were the reverse of those in Figure 2, in that the greatest differences in lather volumes came during the first hour. Although by working quickly independent operators checked the lather values for the same solution on the halfhour, hour, etc., it was not possible to obtain check curves for different soap solutions made from the same cake of soap. This was doubtless due to the difficulty of standardizing
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for oleic acid cannot exist alone in the solution. Later, unknown compounds of more acidic nature result. The aging effect may be attributed to progressive hydrolysis of the solutions, with formation of products hydrated to various degrees. At the second maximum in Curve I the solutions invariably took on the cloudy appearance associated with colloidal solutions of the emulsoid type. Since the saltingout effect of sodium chloride is based on dehydration of the soap film surrounding the emulsion droplets, the salt resistance of the emulsion would vary with the degree of hydration of the emulsifying element. The deleterious effect of carbon dioxide on soap solutions has been recognized ever since the classic researches of Dewar. It may be explained by the equation 2Na01
+ Hz0 f
COz = NazCOs
+ 2H01
the oleic acid then combining with sodium oleate to form more acid soap. The apparently periodic nature of the emulsion curve is of interest, but at present defies all but the most speculative explanation. Johansen4 found that medicinal oils such as Nujol underwent oxidation in the presence of light, with consequent reduction in the interfacial tension between the oil and water. If the oils were kept from light, no change was noted. However, there was no difference in salt resistance of emulsions made with Nujol exposed to light two days and those made
T I M E I N HOURS Figure 1-Salt
Resistance of S o d i u m Oleate Emulsions
exposure to the air during shaking. But it was clearly shown that there were differences in the lather values of the two series greater than could be attributed to experimental error (experimental error was about 15 cc. of lather). There were still wider differences in the lather value of a soap as it aged. It was evident that in order to ascertain which of two soaps had superior lathering qualities both solutions should be made up in a standard manner and several tests made. When a single value for each was taken, one might have been tested a t a time of maximum lather and the other at a minimum. Curve I
11 111
1V V 1H
IIB
Table of Runs SOLUTION RUN Emulsions Dissolving C. P. NaOl At 25' C., with COa and Oz exat 25' C. in gas-free cluded by scrubwater, having 75 cc. of air above 500 cc. bers of soh. during mixing Like I, but with 225 Like I cc. of air above 500 cc. of soin. Like I Like I, but exposed to 0, Like I, but dissolved Tested at 25' C., and aged at 38' C. like I Dissolved at 25O C. R ~ n a t 2 5 ~ Cwith ., with no other preno protection cautions Lathers D i s s o l v i n g commerAt 25'' C., siphons cia1 soap in gas-free fitted with scrubwater at 85' C., havbers ing 75 cc. of air above 500 cc. of soln. during mixing (20 min.) By heating till soap At 25' C.,with no dissolved; uo protecprotection tion SOLUTIOX MADE
RESULT Six solns. gave check values
630 Salt resistance lowered Aged more rapidly Aged faster; salt resistance increased Salt resistance markedly lowered Lather value changed with time
Average value lower than I B
Theory of Aging
According to M ~ B a i n ,sodium ~ oleate solutions first undergo hydrolysis somewhat according to the equation 2Na01 8
+ HzO = NaOl.HO1 + NaOH
J . SOC. Chem. I d . , 37, 249T (1918).
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I
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