August, 1923
IiND V S T R I A L A N D ENGINEERING CHEXISTRY
actual temperatures. Holes were drilled through the tread of the tire to various depths to admit the tire thermocouple. The tire was heated by a sectional air bag through which steam could be passed a t any desired pressure. The results of the calibration of the thermocouples in this manner checked with those previously obtained. Drilling a hole in the tread of a tire to receive the thermocoupltx is not so severe on the tire as one might suppose. After a year's experience using this method in the laboratory, no tire has been found in which premature separation between the plies has occurred due to drilling the hole. In a tire having twelve plies of fabric, the writers have drilled through nine plies and still operated the tire for an extended time. When this method is used on road tests a rubber plug inserted in the hole will exclude all dirt. No rubber cement is necessary to keep the plug in place. When a
845
reading is desired the plug can easily be removed with SE pair of sharp-nose pliers. Two precautions must be taken when using the tire thermocouple in order to secure correct temperature readings. The first is to allow the thermocouple to remain in position long enough to overcome the lag in the thermocouple. This takes about one minute, but varies slightly under different conditions of temperature. The other is the correction necessary for the time of reading after the tire stops. As soon as the tire stops rolling it begins to cool. Since the temperature cannot be taken instantly, it is always necessary to note the exact time of stop and the exact time when the temperature is taken. The rate of cooling of the tire should be observed and from the cooling curve a correction can be made for the drop in temperature between the time when the tire stops rolling and the time when temperature is hken.
Sodiurn Hypochlorite' I-The
Preparation of Concentrated Sodium Hypochlorite Solutions of Great Stability for Use in Food Factories,-Milk Plants, Etc. By Harper F. Zoller THBNIZERLABORATORIES Co., DETROIT,MICH.
ETHODS for the tants. Calcium hypochloA demand for cheap sodium hypochlorite exists in the United preparation of sorite, or chloride of lime, is States because of its rapidly increasing use as a disinfecting agent dium hypochlorite much lesi; used than forin food jactories and elsewhere. are so numerous that it merly, principally because A method for making strong sodium hypochlorite solutions of seems almost unnecessary of the high lime carrying 2 to 5 per cent available chlorine from sodium hydroxide, sodium to add one more to therichly power and the sluggishcarbonate, and drum chlorine is given, and cost data arc presented. laden literature. But the ness of its suspensions. The value of much bu$er material in the holding of the pH around methods heretofore adSodium hypochlorite is 10.5 for the region of maximum stability of concentrated sodium vanced have been of value more effective, is simpler hypochlorite solutions is the principle of a successful method of only t o the textile manuto handle, and will not preparing such solutions. facturw. A specific hypoleave a film of lime a t any The yield of sodium hypochlorite calculated from the weight of chlorite solution was made time through its use. chlorine used is about 100 per cent. This points to a di$erent for a special factory operaMany factories and plants conception of the chlorinating reaction than that which has been tion under a given set of engaged in the production prevalent. working Conditions. No of food,products would use method has been devised for sodium hwochlorite as a the wholesale production of a stable hypochlorite solution sterilizing rinse for their equipment, providedlarge quantities which would be suitable for transportation or storage for use of a uniformly stable quality could be made readily available. in other industries. This study of hypochlorites was under- The present market price is prohibitive to a factory of any taken for the express purpose of determining the true nature size. of hypochlorites in solution, their stability and activity, and 'A careful search into the merits of hypochlorites as sterilof producing a method for their preparation in large or small izing agents under conditions where organic matter was quantrties for industrial plants. mainly absent, a t once revealed their value, and a series of Our conceptions of the constitution and the physical and studies was undertaken to determine suitable methods of chemical behavior of hypochlorite have very materially preparing the one logical hypochlorite (sodium) in large changed in the last few years. Recently, there have been a quantities. These studies led to a consideration of the few attempts to regulate the stability and bleaching prop- practical stability of this substance under the conditions to erties of chlorinated alkali solutions by studying their alka- which it would be subjected in food factories and elsewhere, linity in an empirical fashion. Among these investigations as distinguished from the properties expected of it as a are the observations of Higgins2that alkalies stabilize sodium textile bleaching agent. hypochlorite solutions and lower the velocity of bleaching, A method is here outlined which will enable the average while neutral salts increase the bleaching rate and decrease factory to prepare its own effective disinfecting agent simply the stability. Renewed interest in hypochlorites, especially and cheaply. In subsequent papers the writer will take the alhdi hypochlorites, for bleaching purposes in the textile up the activity of sodium hypochlorite in the presence of industry has been strongly manifested in England during the organic matter and its relative bactericidal efficiency. The last decade. I n the United States the pendulum seems to have method described in this paper is based upon the hydrogenswung in another direction; we have become deeply interested ion control system of manufacture. The solution is heavily in hypochlorites as sterilizing agents and general disinfec- buffered in order that the reaction of the solution will not rapidly change to yield an unstable solution. A sodium 1 Received December 18, 1922. hypochlorite solution containing 5 per cent available chlorine * J . SOC.Chem. Ind., 27, 185 (1911).
INDUSTRIAL A N D ENGINEERING CHEMISTRY
846
is here considered to be a concentrated solution. Solutions containing 10 and even 15 per cent available chlorine are readily prepared using the same principle, but they are unwieldy and impractical for general use. STABILITYOF SODIUM HYPOCHLORITE The first successful attempts to prepare stable, dilute hypochlorite solutions for purposes other than bleaching were attempts those of D ~ i k i nand , ~ Cullen and A ~ s t i n . These ~ matured in the introduction of a serviceable antiseptic solution for medicinal and similar uses. But, owing to difficulties co-existent with the transportation and application of the Carrel-Dakin solution, a series of chloramines was developed which has in a measure superseded the Dakin solution. Cullen and Austin found that between pH 9 and 10, Dakin’s solution is very stable. This solution of sodium hypochlorite approximates a 0.44 per cent solution of available chlorine, or a 0.45 per cent solution of sodium hypochlorite. Many attempts by others to prepare more concentrated soIutiona of sodium hypochlorite at a supposedly similar range of hydrogen-ion concentration (pH 9 to 10) havemet with failure, the reason being, in the writer’s estimation, a poorly buffered solution at the concentration sought. It is absolutely essential that the solution be heavily buffered between these limits of p H if a high concentration of hypochlorite is desired. The methods in general use for the preparation of sodium hypochlorite are: ( a ) Double decomposition of calcium hypochlorite (chloride of limc ) with sodium carbonate or sodium sulfate. Electrolysis of sodium chloride with the production of sodium hypochlorite and hydrogen. (c) Direct chlorination of sodium carbonate with chlorine gas.
(e)
Wherever large quantities of sodium hypochlorite are demanded, the first process is undesirable because of the variable character of commercial chloride of lime, and because of the large mass of residual calcium carbonate sludge which must be disposed of. In the electrolytic method it would be necessary to employ buffers along with the sodium chloride if a strong solution of sodium hypochlorite were desired; otherwise, it would be extremely unstable and the tax on the electrodes and equipment enormous. The direct chlorination method is the most practical one for universal practice of producing strong sodium hypochlorite solutions. It is the most easily controlled and can be made rapidly on a commercial scale. I n adopting the direct chlorination method of manufacture, the first step was to provide a solution with sufficient buffer material to hold the hydrogen-ion concentration in the region of p H 10 to 10.8. On the assumption that the zone of reaction required for the stability of Dakin’s solution was applicable to stronger solutions of sodium hypochlorite, several preparations of 2, 3, 3.5, 5, and 10 per cent available chlorine were made and studied in regard to their stability. The results of the study showed that for maximum stability these strong solutions required that powdered phenolphthalein spread on their surfaces should show a faint but distinctly red color, and further, that a 1 per cent alcoholic solution of thymolphthalein should show a flash of blue color. When such a solution is analyzed for titrable alkalinity, available chlorine, and total chlorides, and calculations of the true hydrogenion concentration are made therefrom according to the scheme suggested by Cullen,4 one finds that the reaction is in the region of p H 10 to 10.6. This is a higher pH than is desired for Dakin’s solution. The quality and quantities of buffer materials used for the purpose of furnishing the necessary a Dakin, Brit. Med. J . . 11, 318, 1911; Dakin and Dunham, “Handbook of Disinfectant
.”
4
Cullen and Austin, J Bzol. Chem., 34, 553 (1918).
Vol. 15, No. 8
reserve alkalinity follow later in the section devoted to the specifications for the hypochlorite preparation. The following table is compiled from a great mass of trial runs made to determine the correct quantities of alkalies and pH for optimum stability: 60% Caustic Ash
Anhydrous Soda Ash
%
%
5 5 5 5 5 5 5 5 2.5 2.5 2 . 5, 7.5 7.5 7.5 7.5 12.5 12.5
5 5 5 7.5 2.5 2.5 2.5 5 2.5 2.5 2.5 5 5 ’ 2.5 2.5 2.5 2.5 2.5 2.5 5
10
10 10 5 5
0 0
TABLEI ApproxiAvailimate pH Pink t o able Calcd. wheA PhenolChlorine Freshly phthalein % Ma4e (Powdered) 3.15 8.5 No 3.03 9.0 No 4.22 7.8 No 3.20 8.8 No 2.53 9.8 Yes 2.30 10.2 Yes 2.20 Yes 10.8 -2.50 Yes 9.8 2.00 9.0 No 1.65 9.8 Yes Yes 1 50 10.4 Yes 4.05 9.4 3.50 10.5 Yes 10.2 3.30 Yes 3.20 Yes 10.6 Yes 9.8 6.50 Yes 10.2 6.00 5.00 Yes 9.5 10.0 4.50 Yes 5.00 10.0 Yes 2.05 No 0) 1.50 Yes (?) I
BIue Flash Available ThymolChlorine phthalein, after Alcoholic 10 Days 1% % No 1.72 2.10 No No 0.70 No 2.04 2.28 No 2.29 Yes 2.20 Yes 2.45 No 1.20 No Faint 1.58 Yes 1.51 3.40 N O Yes 3.48 Yes 3.30 Yes 3.20 6.29 No Yes 6.00 4.80 No Yes 4.51 Yes 4.96 0.12 h70 Yes 1.10
While all the buffer materials were serviceable, sodium carbonate, because of its availability and cheapness, proved superior. As far as could be estimated, there was no appreciable anion influence on the stability of the concentrated solutions among the above buffers. The criterion of the stability seemed to be the intensity of the alkalinity, which is here characterized as the hydrogen-ion concentration. ’ RELATIVE EFFECTOF BURRERMATERIAL (ANIONS) O N T H E STABILITY OF SODIUM HYPOCHLORITC
TABLE11-SHOWING 60%. Caustic
Ash %
715 7.5 7.5 7.5 7.5
% Bu+r
Pink to Blue Flash on Mow- Powdered to 1% ture-Free PhenolThymolBuffer Basis phthalein Phthalein NanCOa 2.5 Yes Yes NaaPO4 2.5 Yes Yes NaaBdO? 2.5 Yes (7) NaaSiOa 2.5 Yes Yes NaHCOs 2.5 No No
Available Available Chlorine Chlorine 30 Days Fresh Later
%
%
3.25 3.19 3.20 3.22 3.25
3.25 3.17 3.21 3.22 2.80
The influence of daylight on the stability is only minor. The use of amber-colored bottles is unnecessary. I n ordinary clear glass bottles the hypochlorite solutions keep for 5 or 6 months with less than 10 per cent loss in available chlorine. It is not necessary either to cool the alkali solutions below 40” C. while chlorinating them, or to store the resulting hypochlorite in a cold place. Whereas it is true that the activity of the hypochlorite solutions (chlorinating power) is accelerated by small increases in temperature, their internal decomposition is not noticeably accelerated a t the stable region in p H 10 to 10.5. QUANTITATIVE ASPECTSOF
THE
CHLORINE-GAS METHOD
When chlorine gas is passed into a mixed solution of sodium hydroxide and sodium carbonate, containing about 10 and 2.5 per cent, respectively, and the gas is stopped when the solution registers 5 per cent of available chlorine, it is found that the yield is 99 to 100 per cent. A temperature change from 1 5 O to 40” C. does not affect this yield. There is no formation of either chlorate of perchlorate under these conditions, or, if there is a chance formation of one or both, they must revert immediately to the hypochlorite, since the chlorine is found in the available condition in the solution. As a matter of fact, when the sodium hypochlorite solution is titrated for the available chlorine concentration, with sodium thiosulfate and sodium iodide in acid solution, actually two equivalents are titrated for every mol (70.9 grams) of chlorine gas passed into the alkaIine solution. It matters not whether these equivalents come from the bound oxygen or bound chlorine in the hypochlorite molecule, so long as experience
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
August, 1923
shows that the complete activity of the hypochlorite solution is not destroyed before it registers zero available chlorine. In actual experience a pure sodium hypochlorite solution a t p H 13 begins to lose free oxygen to the air. The higher the temperature a t this p H the more rapid is the decomposition. Coincident with this loss of oxygen the solution becomes more acid, and because of the increased acidity the decomposition is again hastened. It is an example of catalysis augmented by the hydrogen ion. Whether or not it is the chlorine or the oxygen, or both, which are the active constituents of sodium hypochlorite, for eveTy pound of chlorine used, one pound (100 per cent) of available chlorine is obtained in the product.
PREPARATION OF SODIUM HYPOCHLORITE UNCIILORINATED SOLUTIOW-It was found desirable to use sodium hydroxide of good technical grade (60 per cent caustic ash) for chlorinating, and a good grade of soda ash (anhydrous sodium carbonate) for the buffer material. I n order to make a solution of sodium hypochlorite of certain strength, a definite amount of alkali in the presence of the buffer will be required to maintain the stable point in pH. Astronger solution will require more alkali. The writer has made several thousand gallons of 2.5 to 5 per cent sodium hypochlorite during the last two years, and has found it desirable to maintain the concentration of sodium carbonate at the same point in all the formulas-viz., 2.5 per cent. TABLE 11-SHOWING FOR
NaOH (60% Free Alkali) % 2.5 5.0 7.5 10.0 12.5 I ”
R E L A T I V E AMOUNTS OF ALKALI A N D ALKALI CARBONATF. DIFFFRENT CONCENTRATIONS OF PRODUCT
NaaCOs Average Chlorine pH (Anhydrous Soda Ash) for Stable Product (Approx.) 74 % 7”
i2 .:55
2.5 2.5 2.5
1.4 2.25 3.25 4.50 6.25
1o:a
10.8 10.5 10.5 10.6
842
liberated iodine is titrated directly with the thiosulfate t o the disappearance of the yellow color. No starch paste is necessary, although a white paper background is convenient, The number of cubic centimeters of 0.1 N sodium thiosulfate required for the 2 cc. of chlorinated solution, multfplied by the factor 0.1772, will give the percentage of available chlorine in the sodium hypochlorite. The percentage of available chlorine multiplied by 1.05 is the percentage of sodium hypochlorite in the solution. It is very essential that the difference between the concentration of available chlorine and concentration of sodium hypochlorite be specifically stated. The two are often intermingled. RELATIVECOSTSOF PRODUCTION The overhead expense of this method of manufacture is very low. Soda ash and caustic soda are relatively cheapthe former is around 2 cents per pound, and the latter about 4 cents per pound. Drum chlorine is quoted a t 7 to 10 cents per pound. Thus, if we allow 50 per cent for labor costs, the expense of producing 2.5 to 5 per cent “available chlorine” sodium hypochlorite amounts to approximately 6.80 cents and 16.22 cents per gallon, respectively. These values are in a marked contrast with the price of some of the commercial sodium hypochlorite preparations now on the market.
Dimensions of Beakers and Flasks A conference on standardization of dimensions of glass beakers and flasks held a t the Bureau of Standards January 28, 1922, was attended by representatives of the American Chemical Society, the Manufacturing Chemists Association, the Association of Scientific Apparatus Makers of the United States of America, several government departments, and each of the manufacturers of glass beakers and flasks in the United States. The discussion led to the approval of the selection of sizes recommended in t h e published report1 of the Committee on Guaranteed Reagents and Standard Apparatus of the American Chemical Society. A definition of capacity was adopted that is in accordance with long-established custom in the glass-blowing industry. It provides that the vessels shall hold between 10 and 20 per cent over the nominal capacity. A subcommittee was appointed with authority of the conference to decide in detail on the dimensions. This committee consisted of representatives of the three associations named above and representatives of all the manufacturers. It had been generally agreed that no radical changes in dimensions were desired. The changes needed were t o permit better nesting of beakers where necessary for shipment and t o correct the capacities of a few of the sizes which were not within the limits adopted. The expense involved in making a Iarge number of changes would be all out of proportion to the benefit derived, because there has been little complaint in the past with reference t o the dimensions of beakers and flasks. The subcommittee had a meeting in New York to discuss the best way of coming to a decision on the different items. Data from the manufacturers were later compared and a tentative set of dimensions prepared for further consideration. At a final meeting of the subcommittee held in U’ashington April 30, 1923, a modification of this set of dimensions was adopted. The manufacturers of beakers and flasks have proceeded to change their molds as required to bring the dimensions of the different articles within 1 or 2 millimeters of the standards set. The changes are in nearly every instance so slight that very few users will notice t h a t any changes have been made. Vessels from different manufacturers will, however, be more nearly of the same size, beakers will nest better, and the relation between actual and nominal capacity will be more uniform. The exact dimensions selected can be obtained from the secretary of the subcommittee, W. D. Collins, U. S. Geological Survey, Washington, D. C. 1 THIS JOURNAL, lS, 1070 (1921).
For 5 to 25-gallon quantities of hypochlorite, the alkali and soda ash are weighed into an iron or copper bucket, and about one-third to one-half of the water is added and the whole stirred until dissolved. It is then filtered through layers of absorbent cotton or muslin into the chlorinating receptacle, which should contain the remainder of the water. CHLORINATION-The chlorine is led from a commercial drum through a copper tube fitted with a brass or bronze needle valve, and silver soldered thereto. The copper tube may be made to fit snugly into the valve head on the chlorine drum and clamped there under pressure. The copper tube from the needle valve terminates into a gas meter, which is chlorine-tight. The meter may be either of the dump type or Venturi effect. Both have been used with success. They must be made entirely of glass and filled with a nonfreezing, nonchlorine-attacking solution such as an alkali chloride brine (MaC1). If rubber connections are used they will have to be frequently replaced. A chlorine distributor for immersion into the alkali solution may be made from a coarse alundum thimble and glass tube. Similar diffusers are already on the market. By aid of the needle valve the stream of chlorine gas can be easily regulated. For large-quantity production the chlorine meter may be dispensed with, but it is then necessary to follow the rate of chlorination by titration. CONTROLO F STRENGTHO F HYPOCHLORITE-It iS Only necessary to know the quantity of chlorine passing into the alkali during a given time interval to calculate the strength in terms of available chlorine. However, it is often more convenient to have available a 0.1 N sodium thiosulfate solution for the purpose of direct determination of the available chlorine content. The method used in this laboratory is to measThe University of Chicago has announced a gift of $200,000 ure 10 cc. of distilled water, 5 cc. of glacial acetic acid, and from the Seymour Coman estate, the income t o be used for 5 cc. of 5 per cent sodium iodide into a Erlenmeyer flask. “scientific research, with special reference to preventive medicine Exactly 2 cc. of the hypochlorite solution are added, and the and the cause, prevention, and cure of diseases.”
