INDUSTRIAL A N D ENGIYEERING CHEMISTRY
972
through for each run, and it was determined that if the rate of flow was adjusted to about 1 liter in 8 or 10 minutes complete saturation was a,ssured. This was ascertained by passing air through at different rates. Table 11-Vapor OSSD.
TEMP.
c.
Pressures of Pentachloroethane
VAPOR PRESSURE OBSD.
Mm.
TEMP.
c.
VAPOR PRESSURE
CALCD.~ Mm.
L'APOR PRESSURE OBSD. FROM CCRVE
M m, 2.5 3.5 4.5 6.0
a
Calculated by means of equation:
log P = 7.80304
8.0 10.0 13.0 16.0 20.0 25.6 32.0 39.0 48.0 59.0 72.0 87.0 105.0 125.0 148.5 178.0 209 5 245.3 288.2 334.0 386.5 447.0 512.5 586,O 670.0 764.0 870.0 2129.6
F'ol. 22, s o . 9
similar to that used for the compound, which was submerged in the same low-temperature bath, before going into the air saturation train. The vapor pressure was calculated by means of the following formula based on Dalton's laws of partial pressures: w VcTP760 Vapor pressure (mm.) = 760 wVsT 273Vp w = weight. in grams Vs = spehfic vohme = 22.41/M.W. = 0.09489 liter per gram P = barometric pressure, in mm. V = volume of air, in liters T = absolute temperature of air in aspirator = pressure of air in aspirator, in mm.
+
Table I11 shows the results obtained on hexachloroethane. Table 111-Vapor Pressures of Hexachloroethane VAPORPRESSURE TEMPERATURE VAPORPRESSURE TEMPERATURE c. Mm. c. Mm. 15 0.15a 40 1.OOb 20 0.22a 45 1.49b 25 0.32a 50 2.12b 31 0.55b 55 2.93b 35 0.70b 60 4.105 a Pressures obtained from curve. b Pressures obtained from experiment.
Importance in Fumigation Work
- T(abs.) -
The saturated air was then passed into a U-tube condenser partly submerged in carbon dioxide snow-ether slush having a temperature of about -78" C. At this temperature the hexachloroethane has no appreciable vapor pressure, and is thus completely condensed. The intake end of the condenser system extended inside the air saturation train to a point well below the surface of the constant-temperature bath. It is obvious that the air used for these experiments must be thoroughly dry, otherwise, not only hexachloroethane, but also water will condense in the low-temperature condenser ( 3 ) . For this reason the air was passed through a calcium chloride tower, then through a condenser tube,
I n fumigating work it is essential to know how much of a certain fumigant can vaporize into a fumigating chamber of a given size. I n the previous publications on vapor pressures of fumigants formulas were given whereby these calculations could be made. The same formulas may of course be applied to the compounds discussed in this paper. It must be remembered, however, that the results obtained by the use of these formulas do not take into account losses due to faulty fumigating chambers or adsorption of the fumigant on the surfaces of the materials within the chamber. Literature Cited (1) Neifert, Cook, Roark, Tonkin, Back, and Cotton, U. S. Dept. Agr., Bull. 1313 (1925). (2) Xelson, IND. ENG.CHEM.,20, 1380, 1382 (1928); 21, 321 (1929). (3) Nelson and Hulett, I b i d . , 12, 40 (1920). (4) Parker and Long, Bull. Bur. Bio-lech., 4, 102 (1921). (5) Roark and Cotton, J. Econ. Enfomol., 20, 636 (1927); 21, 135 (1928). (6) Tattersfield and Roberts, J. Agr. Sci., 10, 199 (1920).
Some Less Familiar Applications of Soluble Silicates1 James G. Vail PHILADELPHIA QUAWI"C COMPANY,
121 SOUTH THIRDST., PHILADELPHIA,P A .
ILICATE solutions of the same NazO content may vary widely in pH. A tenth-molar solution, for instance, may show anything between 10.8 and 12.4 (2, 9) according to the ratio between NazO and SiOz assuming the limits to be NasO :SiOz (sodium metasilicate) on the alkaline side and NazO:4Si02 on the side of highest silica content. As a matter of fact these limits, which have been set for industrial convenience, are not impassable boundaries, for sodium orthosilicate, 2Naz0:SiOn, is known, and in relatively dilute solution diminishing amounts of alkali may be present until one containing only colloidal silica is reached. It is possible to make a silica solution a t any desired pH and to traverse the range from 9 to 14 without being bound by narrow limits of concentration. A twice-normal solution of sodium metasilicate has a pH of about 13.4. The degree of hydrolysis
S
* Received June 14, 1980.
varies, but it is always low in comparison with the hydroxylion concentration in corresponding sodium hydroxide solutions. For ratios more siliceous than 1:1, and concentrations above molar, i t is less than 6 per cent. The strong buffer action of the silica also makes it possible to meet a variety of requirements. These and other phases of the adaptability of silicate solutions have led to some strange proposals for their use. The excuse for gathering here some of the less familiar applications is that they may contain suggestions for solving other problems. Treatment of Ripe Olives
The process of making ripe olives fit to eat includes treating them in a solution of caustic soda. Relative to the green olives on the market the fruit is ripe, but the degree of ripeness permissible is limited by the softness of the cured olives.
September. 1930
INDUSTRIAL A N D ENGINEEMKG CHEMISTRY
They may be allowed to ripen further on the tree and still yield a 6rm texture if the action of the alkali is modified by substituting sodium metasilicate for caustic. The flavor of the fruit is better and the process yields a product which a p pears to be entirely acceptable. The writer does not know how much castile soap we ordinarily eat with ripe olives, but the degree of saponification with metasilicate will be less than in the older process.
973
Uses Due tu Corrosion Resistance
Corrosion and its prevention account for numerous uses of soluble silicates. Ordinitry shaving creams (4) with a soap base, and various alkaline cosmeticswill attack an aluminum tube and in many cases cause its failure in a few weeks a t temperatures well within the range of atmospheric exposures. Small additions, less than 0.5 per cent, of the more
Flpure I-Sodlurn Silicate Inhibition of Corroslan in Nurnlnurn Tvbee Due to Shaving Soap The coiraied piece on thc left is a dull gmyfsh white: the protected tubes are brilliantly lustrous.
Uses Due to Hi&h pH
A Iiigh pH with a maximum alkali reserve is desirable in the treatment of certain intestinal diseases. Destruction of tissue must be avoided. Hepburn and Eherhard (IO, I I ) studied buffer solutions and found sodium metasilicate capable of neutralizing more than twenty times as much lactic acid as a citrate buffer when titrating to a pH of 7. This same characteristic has its use in modern laundering and other cleansing operations of industry, where the nature of the work cause8 partial neutralization and the maintenance of a high pH makes for efficiency. Alkalinity is obviously not the only factor which affects the bactericidal action of detergent solutions, hut it has recently been shown (17) that a pH above 12 at a temperature of 60" C . is sufficient to insure the d e struetion of B. coli and mycobacterium tuberculosis within 5 minutes. Applied to the washing of milk bottles, this means that the correct conditions may be had with solutions of sodium metasilicate without danger of etching or destroying the gloss of glassware, as would be the case if caustic soda solutions of equivalent alkalinity were used. Sodium metasilicate is now available as a freeflowing granular solid readily soluble in cold or hot water. This is entirely different from the difficultly soluble anhydrous Elasses or even from the hydrated powders of silica &io above that of the metasilicate, NaBiOa. On the acid side of 7 there is a tooth paste (7) on the market made from a silicate solution acidified with fruit acids to yield a pH of 3.6 in use. I t looks like a soft jelly, has a savory taste and smell, and is advertised as a dissolving tooth paste. This is not the place to argue the merits of dentifrices, acid or alkaline, but it illustrates the possibility of producing from silicate solutions non-fiowing media of acid as well as alkaline character, with or without additions, for such purposes as textile printing, growing of bacteria or molds, making nonspilling electrolytes for storage batteries. a,? well as the ordinary manufacture of silica 91 ..
siliceous types of silicate solutions will stop this action so completely that the metal remains bright after many months. (Figure 1) The effect of much larger silicate additions than are needed to stop corrosion has been tested by supplying them for regular use to men who did not know their composition. Some noticed a more abundant lather, but no unfavorable criticism developed. The advantage of aluminum tubes is thus released to a much more extensive use with the help of silicate solutions. The value of silicate for preventing corrosion of aluminum by alkaline cleansers is becoming well known. It depends on film formation at the metal surface. Similar effects are secured to prevent rusting of iron in domestic hot-water-supply systems (18), and the dissolving of iron and lead in municipal water supplies (19) can he almost completely suppressed by adding silica to tho water, most conveniently as a sodium silicate. Another effect, not yet sufficiently known, is the resistance to acid corrosion which can be imparted to such materials as Portland cement, or even ordinary red brick, by saturating them with silicate solutions sufficiently dilute to penetrate. (Figure 2) The action is partly due to filling up of porous structures, but the formation of insoluble silicates also plays a part. The ability to impart increased life, and increased resistance to abrasion and penetration of oil or water, to concrete surfaces such as floors and roadways still belongs in the category of less familiar uses in the sense that the opportunities to take advantage of these properties of silicate solutions are much more widespread than the information. Protection against Fungus Invasion
Protection of tree wounds against fungus invasion (88) may be counted as an unusual, a t least an unexpected, use for silicate solutions. It has, however, been found that painting the freshly exposed surface with a viscous silicate of s type high in silica prevents undue loss of say, and secures the surface against destructive growths.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
974
Intluence of Silicates in Modifying Chemical Reactions
Tliere is a group of uses of silicate solutions which depend upon their influence in modifying chemical reactions. Some of them have been empirically arrived at and remain unexplained. For instance, in the curing of logwood preparatory to extracting the coloring matter a fermentation of the moist chips is practiced. A light sprinkling with a silicate solution ( I ) causes the color to diffuse toward the surface of the pieces and facilitates extraction. A pyrethrum soap spray (20) has been found effective against the Japanese boetle and some other insect pests. Its activity is greater when it contains silicate of soda. Whether the silicate functions tolncrease the wetting power of the spray or to act as a stabilizer of the emulsion is not known. Though not toxic itself, it may provide through buffer action the riglit alkalinity to give the best effect of tlie active poison.
. Figure 2-Effect of Silicate Treatment on Brick Exposed to 10 Per Cenr Sulfuric Acid for 18 Days at 90" c.
Val. 22. No. 9
combine with the sodium of sodium silicates, will accomplish similar results, but mechanical strength requires that the gel be formed in situ, to accomplish which the reaction must not occur in such a way that the gel is disturbed after it is formed. Thus a precipitant which reacts slowly is usually required. A recent process for consolidating quicksands (14), however, makes use of calcium chloride which reacts very q6ickly. The silicate is first pumped into the sand and the precipitant follows under substantial pressure. The gel solidifies foundations and seals the sands against the flow of water. An older process (6) uses the gelatinous precipitate from dilute aluminum sulfate with silicate to lubricate and imarove the aenetration of cement susaensions into aorous rook and fissures. Precipitation of silicate solutions with metallic salts vields a great Lumber of products with the curious property or base exchange. This has been extensively applied to the making of products for softening water after the manner of the socalled zeolites. The facility with which metals of the alkaline earth and alkali groups can be removed from solutions and recovered in soluble forms suggests undeveloped possibilities in the chemical industry. An interesting process in which precipitation with silicate solutions is employed to purify molasses is used to obtain a cheaper nutritive liquid in which to grow yeast (12). Crude molasses yields yeasts of unsatisfactory color which impart unsavory flavor to bread. The silicate precipitates, however, appear to remove the constituents which are objectionable and a quality product is more cheapIy produced than with the usual extracts of malted grains. Another precipitation reaction is that employed to set the silicate paints used to color incandescent lamp globes (8, fr6). A silicate paint is sprayed on and dried, then dipped in a solution of ammonium sulfate, which reacts with the silicate and makes the film insoluble. On account of the colorless nature of the vehicle, a silicate paint has shown the highest reflecting power for pliotometric apparatus.
Left. treated with dilute neutral silicate: right un. Note deposit of decomposed brick in 6ttcr
Conclusion
treated.
ShmPie.
Silicate solutions enable hydrogen peroxide hatlis (21) to exert a maxirnurn bleaching cffect with mininium loss of oxygen. This behavior is distinct from the alkalinity the silicate imparts, and the results are better than those obtained with other alkalies. Additions of sodium silicate solutions, as inorganic colloids, to chromium-plating baths is said to yield bright, adherent coatings a t current densities as much as 15 amperespersquare decimeter above the usual levels (3). Similarly, for producing smooth, dense electrolytic deposits an dkaline siiicate and sulfuric acid may be employed in the electrolytic refining of copper (16). I n such a case, of course, the added substances must be such that. there are produecd no appreciable quantities of foreign ions having a disturbing influence on the electrolysis. Soil phosphatcs become more available for plant growth when soluble silicates are present ( 5 ) , increasing yields of both grain and straw from the barley. There may be cases where this is significant for agriculture, as the gains were as great as 25 per cent without phosphate additions and much smaller, though slill definit,e, when phospha1,es were used. A great diversity of cements which depend on the bonding action of silicate solutions finds appplication for refractory purposes or acid resistance in almost every laboratory or plant. Recent patents (18) describe a self-setting cement prepared as a dry ponder with finely divided silicon which, reacting with the silicate, causes the transition from silica solution to gel. This produces a set without drying and makes a mass practically insoluble in water and wids. Other ingredients, including the more soluble f o r m of silica, which
The scope of this paper prohibits either detailed description or a complete catalog but enough has beeii said to suggest a field of undeveloped uses for soluble silicates as buffers, binders, formers of protective films and gels, precipitants, and cheniical reagents, vithout touching upon their important uses as detergents and adhesives. Literature Cited (11 American Dyewood Co., Peisonal eommudchtion. (21 Bonwe. J. Am. Chrm. So&. Sl, 2575 l10201. Chrom-ha.. Wommer, Fkn& Patent 635,700 (September 6, 1929) J . Sac. Cham. lnd., 19A,290 (1930). Churchill, Am. Inst. Mining Met. Egg, Tmh. Pu6. 116, 3 (1929) Fisher, J . API. Sci.. 19. 132 (19291. Francois. U:S. Pa& 1,391,678' (September 27. 19211; 1.430 306
(15) (161 (171 (18)
(191
C20) (211
(221
(Septrmbei 26, 19221. Frcng, Britirh P a t a t 203,248 (September G, 1923). nageman and Schmid, U.S. Patent 1,581,732 (April 20, 19261. Hsrmho, J . P h x Chrm.. SO, 1100 (1926). Hepburn, J . A m . Diel. Arsam.. 1, 55 (1926). Hepbsrn and Eberhard. Am. J. Mcd. Sci., 166, 244 (1923). Honman. Frey, and Menill, u. S . Patent 1,087,581 (October 16. 19281. I. G. Parbenindurtrie, German Patest 4G0.125 (May 3, 1928); 460 813 (May 18, 1928). Jooeten. Ceimrn Patent 441,622 (March 9. 1927); British Patent 322,182 (Ma7 24. 192.31. Luckicrh, U. Sy P&nt 1.'4G4.101 (August 7, 19231. Mctallgeseii~chaft,A. G.,British Pstent 299,725 (October 29, 1028 Mudgc, Food I d , 1, 613 (19201. Speller. U. S. Patent 1,531,992 (March 31. 19251. Thresh. "Eramination of Waters and Water Supplies," p. 128, B.ak too, 1926. U.S . Dept. Agr.. Yearbook of Agriculture lor 1928.p. 87. Weber, 1.See. Dyers Colouristir. OW, 209 (19231. Young. Ohio A s . Expt. Sta.. BUN. 8. 13 (19231.
