68
INDUSTRIAL AND ENGINEERING CHEMISTRY
gram normal weight that a chemist after using it but once is convinced of the reasonableness and advantage of this improvement. The consumption of sugar in Egypt, which was 160,000 metric tons per year at the time of my visit in 1930, has since decreased to 135,000 tons; the production, which was only about 100,000 tons three years ago has now, as a result of favorable government legislation, been increased to 150,000 tons per year, which slightly exceeds the present consumption. This increase in production was easily accomplished by the different plantations making the necessary extension in the areas of land for growing sugar cane. Inasmuch as the sugar industry of Egypt has now succeeded in bringing its production up to the demands of local consumption, which was the main object of the protective policy recently inaugurated by the Egyptian Government, a further expansion of the cane sugar industry of Egypt is not likely to occur under present economic conditions. I n concluding these sketchy personal observations upon the sugar industry in different countries I wish to mention the great cordiality which was extended to me in every country where I made my visitations. It would be impossible to mention the names of all of those to whom I owe obligations. I can only say that as I pursued my journey, which
1-01. 25, No. 1
was without a single unpleasant incident, I came to feel more and more that the sugar chemists and sugar technologists of the world constitute a great brotherhood whose chief tenet is the simple requirement of comradeship, helpfulness, and good will. LITERATURE CITED Anonymous, Arch. Suikerind., 32, 459-60 (1924). Ibid., 35, 538-42 (1927). Ganswijk, C. C. W.van, Zbid., 32, 1065-8 (1924). Harreveld, P. van, Ibid., 32, 1095-6 (1924). Inst. for Research in Agr. Eng., Bull. 4, Clarendon Press, Oxford, England, 1929. Kaufman, H . J., Arch. Suikerind., 32, 359-67 (1924). Kriiger, Ts’., “Das Zuckerrohr und seine Kultur.” Magdeburg, 1899. Kriiger, W., and collaborators, “Ernahrungsverhaltnisse, Anbau, Diingung und Krankheiten der Zuckerriibe,” Bernburg, 1927. Rodziewicz, A , , Gaz. Cukrownicra, 68, 133-5; L h t y Cukrovar. 49, No. 26, Rozhledy 24 (1931). Saillard, E., L a . Planter, 78, 469-71 (1927). Schott, G. J., and Harreveld, P. van, Arch. SuLkeririd., 32; Mededeel. Proefstation Java-Suikerind., No. 14, 449-63 (1924). Seite, G. E. G. yon, -4rch. Suikerind., 28, 519-33 (1920). RECEIVEDBpril 6, 1932. Presented before t h e Division of Sugar Chemistry a t the 83rd Meeting of the American Chemical Society, New Orleans, La., &arch 28 t o April 1, 1932.
Gel Formation in Sodium Metasilicate Solutions M. J. PRUCHA AND C. A. GETZ, College of Agriculture, University of Illinois, Urbana, Ill.
S
ODIUM HYDROXIDE, trisodium phosphate, sodium combinations of them were studied as to their influence on carbonate, and sodium bicarbonate, used singly or mixed gel formation in sodium metasilicate solutions: in varying proportions, have been the principal ingrediAddition of lactic acid ents of the alkaline detergents used in dairy plants for cleaning Addition of other alkaline washing powders Addition of sour milk and sweet skim milk purposes. Recently another compound has been added to formation in other alkaline washing solutions in presence this list of detergents-namely, sodium metasilicate. This of Gel milk compound is especially recommended for the washing of Addition of other alkaline washing powder, sour milk, and milk bottles in the soaker-type bottle washer. milk solids Effect of agitation According to Vail (I), sodium metasilicate is an excellent Effect of temperature detergent, and in some respects is superior to the other detergents commonly used. However, an objection has been The experiments were carried out in the laboratory as raised against its use in the soaker-type bottle washer on the follows: Pyrex glass flasks were used for the solutions. To ground that the washing solutions may form a gel. varying concentrations of sodium metasilicate solutions were The knowledge as regards gel formation in silicate solutions added different amounts of lactic acid, sour milk, milk powder, is fully summarized by Vail ( 2 ) . Nevertheless, it seemed and the different washing powders. Each addition of the desirable to undertake a study to determine what factors above substances was followed by a vigorous shaking. The may cause gel formation in sodium metasilicate washing solutions were allowed to stand for a certain number of hours solutions when used in dairy operations. and then observations as to gel formation were recorded. The practice as regards the use and care of the washing The sodium metasilicate used had the composition NazSiOp solutions in the bottle washers varies in different milk plants. 5Hz0. I n some cases a fresh solution is prepared daily, whereas in The results of the experiments are summarized in Tables I other plants the same solution is used day after day for a to X. The following characters were used in the tables to month or longer. The strength of the washing solution is designate the condition of the solutions studied as regards maintained by occasional additions of the detergent. Under gel formation: such practices there will gradually accumulate in the washing - denotes no gel formation solution a considerable amount of milk solids and of acid * denotes a tendency to gel + denotes a weak gel (mostly lactic) from the milk that adheres to the walls of denotes a strong gel the bottles. Another common Dractice in some Dlants is to mepare EFFECTO F LACTICACID ON GEL FORMATION I N aODIUM washing solutions b y mixing two or more of the different METASILICATE SOLUTIONS washing powders in varying proportions for the purpose of I n this experiment, the results of which are given in Table I, improving the cleansing properties of the solutions. I n view of these varied practices, the following factors and Lvarying amounts of lactic acid were mixed with sodium meta-
++
I ND U S T R I A L h N D E N G I N E E R I NG C H E M I S T R Y
January, 1933
69
IN SODIUM METASILICATE SOLUTIONS TABLEI. EFFECTOF LACTICACID ON GEL FORMATION
LACTIC 7 ACID 0 . 5
% 0 1 2 3 4 5
6
6
9 lo
--
-
1
--
1.5
2
3
4
PERCENTAQE CONCENTRATION OF S O D I U M 5 6 7 8 9 10
-
*
++
++ ++ ++ ++ +
--
* ++ ++ ++
++ ++
silicate solutions ranging in strength from 0.5 to 20 per cent. The amounts of acid used ranged from 1 to 10 per cent of 75 per cent strength acid. Lactic acid was used because it gets into the washing solutions from the dairy utensils and equipment during the washing operations. The solutions, after being mixed, were allowed to stand a t room temperature for 24 hours before observations were recorded. It will be observed from Table I that no gel was formed in solutions that were strongly acid, even though they contained more than 2 per cent of sodium metasilicate. No gel was formed in solutions that were strongly alkaline, even after the addition of as much as 10 per cent of the acid. Good gel n-as formed in those solutions which were near neutral point in reaction. As the acidity of the solution was increased, the gel formation became slower, and the gel formed became weaker. When a certain point in reaction was reached, gel formation ceased. I n a similar manner, as the alkalinity in the solution was increased, starting from the neutral point, the formation of gel became slower and the gel became weaker. When a certain point in alkalinity was reached, gel formation ceased. The solutions which were outside the gel-forming zone on the acid side were clear; those on the alkali side had a slight precipitate which was due apparently to the hardness of the water used. In the solutions to which 7 per cent or more of lactic acid was added and which were outside the gel-forming zone on the alkaline side, a copious white crystalline precipitate was formed.
TABLE 11. EFFECT OF BLKALIES ON GELFORMATION I N SODIUM METASILICATE SOLUTIONS ALKALI -PERCENTAGEC O N C E N T R ~ T IOF OISODIUM METASILICATADDED 0 . 5 1 1.5 2 3 4 5
%
TABLE111. EFFECTOF SOURMILK ON GEL FORMATION IN SODIUM METASILICATE SOLGTIONS
EFFECTOF OTHER ALKALINEWASHINGPOWDERS ON GEL FOR?JATION I N SODIUM METASILICATE SOLUTIONS I n this experiment sodiiim hydroxide, trisodium phosphate, sodium carbonate, and sodium bicarbonate were mixed in varying proportions with sodium metasilicate solutions. These were allowed to stand 24 hours before observations were recorded. Table I1 shows that the addition of sodium hydroxide, trisodium phosphate, or sodium carbonate did not cause gel formation in sodium metasilicate solutions. The addition of sodium bicarbonate, on the other hand, caused gel formation in sodium metasilicate solutions that received 4 per cent or more of the bicarbonate. No gel was formed in the solutions that received less than 4 per cent of the bicarbonate.
I n Table IV are presented the results from a similar experiment in which sweet skim milk was used in place of sour milk. TABLEIv. EFFECT OF SWEET SKIM h f I L K ON GEL FORM.4TION IN SODIUX METASILICATE SOLUTIONS SWEET MILK
PBRCENTAGE CONCENTRATION OF SODIUMMETASILICATE 0.5 1 1.5 2 3 4 5
EFFECT OF SOURMILKAND MILKSOLIDS ON GEL FORMATION IX SODIUM METASILICa4TE SOLUTIONS
During the washing operations of milk bottles, a considerable amount of sour milk and milk solids may accumulate in the washing solution. The amount will depend on the number of dirty bottles washed and on the length of time the washing solution is used. I n Table I11 are represented the results from an experiment in which varying amounts of sour milk (from 5 to 100 per cent) were mixed with sodium metasilicate solutions of different concentrations. The mixtures were allowed to stand for about 24 hours a t room temperature before observations on gel formation were made.
In another experiment, the results of which are given in Table V, all the solutions received 30 per cent of sour milk and varying amounts of milk solids in the form of skim milk powder. The sour milk used had an acidity of 0.7 per cent of lactic acid. Thirty per cent of such sour milk contributed to the solutions roughly about 2.8 per cent, of milk solids and 0.25 per cent of lactic acid. Examination of Table I11 shows that gel was formed in 2 and 3 per cent solutions of metasilicate which contained 100
IXDUSTRIAL AND ENGINEERING CHEMISTRY
70
per cent of sour milk. A tendency for gel formation was noticed in 1.5 to 5 per cent solutions containing 50 and 75 per cent of sour milk. (It was difficult to give an exact picture of the condition of the solutions, as regards gel formation, in a tabular form by the use of plus and minus signs.) When sweet skim milk was used in place of sour milk, a better gel formation took place, as seen in Table IV. A gel was formed in 1 per cent metasilicate solution containing 30 per cent milk, and in 1 and 1.5 per cent metasilicate solutions containing 50 per cent milk. A good gel was formed in 1, 1.5, and 2 per cent metasilicate solutions containing 75 and 100 per cent milk. As the concentration of metasilicate was increased, the gels became weaker and the gelatinous matter tended to break up and settle to the bottom. No attempt was made t o determine why better gel formation took place when sweet skim milk was used than when sour milk was used. Apparently the condition of the milk proteins played a part. Gel formation also took place in the solutions containing 30 per cent sour milk and 2 and 3 per cent milk powder, as seen in Table V.
formed especially in 1, 1.5, 2, and 3 per cent solutions that received 30 per cent or more of the milk. As the concentration of the metasilicate increased, the gel tended to change into a gelatinous precipitate. I n solutions of less than one per cent of metasilicate, no gels were formed. Another experiment on this point was set up in which solutions of sodium hydroxide, trisodium phosphate, and sodium metasilicate were prepared, having the same sodium oxide content. To each of these solutions were added 30 per cent of sour milk and 3 per cent of milk powder. The results which are given in Table VI1 show that no gel formation took place in the solutions of sodium hydroxide and of trisodium phosphate. Good gels were formed in metasilicate solutions which contained 0.29, 0.435, and 0.58 per cent of sodium oxide. In the solutions containing only 0.145 per cent of sodium oxide, no gel was formed; in the solutions containing more than 0.58 per cent of sodium oxide, the gel tended to break up into a gelatinous precipitate. TABLEVII. ALKALIES
TABLE v. EFFECTS OF 30 P E R C E X T SOUR MILK P L U S VARYIKQ I N SODIUM 44MOUNTS OF MILK POWDER ON GEL FORMATION METASILICATE SOLUTION MILK
POWDER
P E R C E N T A Q E C O N C E N T R A T I O S O F SODIUM M E T A S I L I C A T E
0.5
1
1.5
2
3
4
5
Vol. 25, No. 1
GEL FORMATION IS SOLUTIONS OF DIFFERENT ALKALIES" NaaO I N 3 0 L U T I o N 0.87 1.16 1 45
P E R C E N T A G E C O N C E N T R A T I O N OF
-
0.29
0.435
-
+
+
0.145
-
-
0.58
-
-
-
-
NaOH NaaPO4.12HzO NazSi03.5HsO These solutions contained 30 per oent Bour milk and 3 per cent milk powder.
-
+
*
*
*
The results in Table VI1 again bring out the fact that gels are formed more readily in sodium metasilicate solutions than in the other alkaline washing-powder solutions in the presence of milk solids. GEL FORMATION IN SODIUM HYDROXIDE AND TRISODIUJI Gel formation in sodium metasilicate solutions containing milk solids appears to be due to two separate factors: (1) to PHOSPHATE SOLUTIONS IS PRESENCE OF MILK the reaction between the alkali and the milk solids, as is I n this experiment sweet skim milk was mixed in varying the case with the solutions of other alkali mashing powders; proportions with solutions of the above alkalies. Observa(2) to the gel-forming property of the metasilicate solution tions were made 24 hours later. itself, which property is not present in the solutions of other It is a well-known fact that, when milk is mixed with solu- alkaline washing powders. tions of alkaline washing powders, a gelatinous matter may be formed, owing apparently to the reaction between the GEL FORMATION I N SODIUM MET.4SILICATE SOLUTIONS I N alkali and the milk proteins. PRESENCE OF OTHER ALKALI WASHINGPOX-DERS, SOUR Table VI shows that a gelatinous precipitate was formed MILK,AND MILKSOLIDS in sodium hydroxide solution when 50 per cent or more of milk was added. I n trisodium phosphate solutions a someAll the solutions in Table VI11 received 30 per cent of sour milk. This amount of sour milk was considered as the maxiwhat better gel formation took place. mum amount that could accumulate in the washing solutions under the most neglected operations. This amount did not TABLEVI. EFFECT OF SWEET SKIMMILK ON GEL FORMATION IN SODIUM HYDROXIDE AND TRISODIUM PHOSPHATE SOLUTIOKS cause gel formation in the metasilicate solutions. The solu-PERCENTAGE C O N C E N T R A T I O N S OF ALKALItions also received 1, 2, and 3 per cent of milk powder. MILK 0 . 5 1 1.5 2 3 4 5 The addition of sodium hydroxide, trisodium phosphate, % or sodium carbonate to sodium metasilicate solutions containing sour milk and milk powder did not seem to increase the tendency of the solutions to form gels. The addition of sodium bicarbonate caused good gel formation. Comparing Tables VI11 and 11,it will be noticed that, when no milk solids or sour milk were present in the metasilicate solution, it required 4 per cent of the sodium bicarbonate for gel formation. On the other hand, a gel was formed in metasilicate solutions containing only 0.5 per cent sodium bicarbonate when the solution also contained 30 per cent of sour milk and 2 per cent of milk powder. This again brings out the point that milk solids increase the tendency in metasilicate solutions to gel formation. The effect of hydrogen-ion concentration on gel formation I n sodium metasilicate solutions (Table IV) a tendency to gel formation was noticed in solutions having only 20 per cent in general is well known. A thorough study of this phase is of milk, and good gels were formed in the solutions having a reserved for future study. The few determinations already higher percentage of milk. From these results it is seen that made show that the milk solids lower the hydrogen-ion conthere is a tendency for gel formation in the solution of all centration of the metasilicate solution. A metasilicate solu three alkalies, but that in the sodium metasilicate solutions tion containing one per cent of milk powder had a pH of 11.9 the tendency is much more pronounced. Good gel was Two per cent of milk powder lowered the pH to 11.2.
January, 1933
I N D U S T R I A L A N D E N G I ?j E E R I N G C H E AI I S T R Y
TABLEVIII. EFFECTOF OTHERWASHINGPOWDERS ON GEL FORMaTION IN SODIUM METASILICATE SOLUTION CONTAININQ 30 PERCEST OF SOURMILKASD VARYING AMOKXTSOF MILK POWDER ~IILK
P E R C E N T A Q E C O S C E N T R < T I O N OF S O D I U M %fETARII~IC.\TE
POWD~R 0.5 % 0
1
1
1 5
2
3
4
TABLEIX. SODIUM
1.5
2
3
0
1
3
3
1
1
70
3
2 3
EFFECTO F AGITATION ON GEL FORMATIOX IZT METASILICATE SOLETIONS CONTAINISG L a C T I C ; ~ C I D AND MILK POWDER .kLH.ALINITY MAINTAINED E Q U I V A L E N T TO THESEP E R CEXTAGEB OF S O D l U h M E T h 8 l L I C A T E :
ACID
9
0
71
4 0 1
2 3 4
0 1 2
3 0 1
2 3
0
1 2 3 0 1 2 3 0 1 2
3 0
I 3 3
0
1
2 3 4
0 1
2 3
4 0
1 2 3
4 0 1
2 3 4
0 1 2
3 4
0
0,s 1 2
3 0 0.5
0
1 2 3 4
was added to neutralize the acid. After vigorous shaking, the solution was allowed to stand 10 minutes, and any tendency for gel formation was observed. This procedure was repeated with each solution until the amount of acid as shown in Table VI was 0 used up. After all the acid was added and this in turn neutral0.5 ized by additions of sodium metasilicate, the final alkalinity of 1 2 each solution was approximately the same as that at the beginning 3 before any acid was added. The sodium oxide content of the solutions was larger at the end than at the beginning of the experiEFFECT OF AGITATION o s GEL FORMATION IN SODIUM META- ment: SILICATE W~SHING SOLUTIONSCONTAININGMILK SOLIDS It was observed in this experiment that, when the solutions AND LACTIC ACID mhich would form a gel (if not disturbed) were shaken interDuring the washing operations of the milk bottles in the mittently, the gel would be broken up to form a gelatinous bottlewashing machinp, the washing solution is violently precipitate. The outstanding point of interest in this experiagitated. When the same solution is used for a number of ment from the commercial standpoint is the fact that a large days, there will gradually accumulate a considerable amount amount of milk solids and of lactic acid was necessary for of milk solids and lactic acid from the dirty bottles. Further- gel formation. more, when the washing solution is used as stated above, it O N GEL FORMATION I N SODIUll is necessary to maintain its strength by occasional additions EFFECTO F TEMPERATURE METASILICATE SOLUTIONS of the washing powder. This experiment, as reported in Table IX, was a n attempt The washing solutions in the bottle washer are usually to duplicate such commercial dairy plant practices and was heated to certain temperatures a t which better washing and carried out in the following manner: sterilizing of the bottles is supposed to be obtained. This experiment was carried out to determine the effect of different In all, eight sets of solutions were prepared. Each set consisted of seven solutions containing, respectively, 0.5, 1.0, 1.5, 2.0, 3.0, temperatures on gel formation in the solutions of metasilicate. For this purpose a mixture was selected from Table X which 4.0, and 5.0 er cent of sodium metasilicate. To each solution was then a d g d a certain amount of milk solids in the form of formed a gel a t 120" F. (48 9' C.) but which was near the skim milk powder. The amounts of milk powder used were 0.1, border line. The solution contained the following ingredi2, 3, 4, 5, 7, and 10 per cent. After the milk powder was dissolved, the solutions were treated ents: 2 per cent of sodium metasilicate; 1 per cent of sodium as follows: A few drops of lactic acid were added and the solution bicarbonate; 1 per cent of milk powder; and 30 per cent of was vigorously shaken. Then a certain amount of metasilicate sour milk. 1
0
3
INDUSTRIAL AND ENGINEERING CHEMISTRY
72
TABLEX. EFFECTOF TEMPERATURE ON GEL FORMATION IN 2 PER CENT SOLUTION OF SODIUM METASILICATE SUBSTANCEB ADDED TO SOLN.
:22il%;%er,(
30% 8our milk
r
32
60
-
-
TEMPERATORE, e F. 70 100 120
-
+
++
140
180
+
t
The solutions were placed a t temperatures of 32", 50°,
70", loo", 120°, 140', and 160' F. (O", lo', 21.1", 37.8", 48.9', 60", and 71.1' C.) and allowed to stay there 24 hours. The solutions kept at 32", 50', and 70" F. did not form gels; the solutions a t loo", 140', and 160" F. formed weak gels; and the solutions a t 120" F. formed strong gels.
CONCLUSIOM 1. Sodium metasilicate solutions do not form gel when no other substance is added. 2. The addition of lactic acid causes gel formation in those solutions which are near neutral point in reaction. The gels become weaker as the acidity or the alkalinity of the solution is increased. Gel formation ceases when a certain point in reaction is reached. 3. The addition of other alkaline washing powders, except that of sodium bicarbonate, does not increase the tendency for gel formation. 4. The addition of sodium bicarbonate causes gel formation. 5. The addition of sour milk and milk solids causes gel formation. The milk solids, as well as the acid, lowers the p H value of the solutions. 6. Agitation tends to break up the gel and thus prevent gel formation to some extent.
Vol. 25, No. 1
7. Temperature of about 120' F. (48.9" C.) causes better gel formation than other temperatures. 8. A certain minimum amount of metasilicate is necessary for gel formation. Best gels are formed in solutions containing 1to 3 per cent of metasilicate. I n solutions having higher percentages of metasilicate, the tendency is for the gel to become a gelatinous precipitate. 9. The amount of sour milk and of milk solids necessary for gel formation is large. It requires a t least 50 per cent of skim milk before a firm gel is formed. A washing solution containing that amount of milk solids, since its reaction is in the gel-forming zone, will have poor cleansing properties. Gel formation in washing solutions may well be considered as a sign of faulty operations. 10. Apparently gel formation in sodium metasilicate washing solutions in the milk bottle washing machines may take place when the solutions contain less than 3 per cent of the metasilicate and when about 4 per cent or more of the milk solids accumulate. Hence, gel formation can be avoided by using solutions that contain not less than 3 per cent of the metasilicate and by discarding the washing solutions before about 4 per cent of milk solids other than fat accumulate in them. LITERATURE CITED (1) Vail, J. G., Paper presented at meeting of Am. In3c Chein. Eng., New Orleans, La., Dee. 8-10, 1930. (2) Vail, J. G., "Soluble Silicates in Industry," A. C. S.Nonograph Series No. 46. Chemical Catalog, 1928. RECEIVED December 11, 1931.
Tests of Chemical Treatments for Control of Sap Stain and Mold in Southern Lumber R. M. LINDGREN,T. C. SCHEFFER,AND A. D. CHAPMAN Bureau of Plant Industry, United States Department of Agriculture, New Orleans, La.
D
URING the seasoning process a t the mill the freshly sawed sapwood of a number of commercially important species of southern woods is subject to permanent discoloration by certain fungi, principally Ceratostomella species and some of the Fungi zmperfecti. Such discolorations have been commonly called blue stains or sap stains because of the color of the portion of the wood attacked. The stain occurs in spots, streaks, or patches of various intensities of color and is due to the dark fungal hyphae which may ramify throughout the sapvood. In addition to stains the fructifications of a number of mold fungi cause discolorations of various hues which are largely superficial in nature and therefore removed in surfacing the wood. The widespread occurrence of these discoloring fungi has been the source of serious annual losses to pine and hardwood lumber manufacturers, especially in the southern region where the climatic conditions are particularly favorable for their development. Such losses are due principally to reductions in grade, value, and marketability of the stained material. Although the stain and mold fungi do not impair the strength of wood seriously, it is evident that their occurrence injures lumber for usks where a natural finish is desired. Recently buyers have come t o discriminate against stained material even in the common grades of lumber,
For some thirty years spasmodic efforts have been made to find an economical means of controlling these fungi in lumber, but not until recently has intensive work been directed a t the problem. Because of its economic importance, this problem was selected in 1928 by the Division of Forest Pathology for concentrated effort. As a result of an estensive survey of existing conditions and mill practices in the southern region, it was evident that of the two general methods in use for preventing stain-namely, the use of chemical dipping treatments or of rapid seasoning practices such as kiln drying, end racking, and steaming-the former would lend itself more readily to improvement. The soda dipping treatment, which was being used by some southern mills to control sap stain, had never proved fully satisfactory on pine and had failed completely on hardwoods. I t was felt that tests of a sufficient number of chemicals would reveal some of greater efficiency and of wider application than past treatments and therefore of immediate practical value to both pine and hardwood manufacturers. The present paper summarizes the results of a number or' such tests conducted over the 3-year period 1929 to 1931.
TESTS Since it was obviously impossible to make tests on SMALL-SCALE
a commercial scale of all the chemicals warranting trial, prelimi-
