silica in solution have been found useful or show promise of useful development. Thus we may examine the service performed as a result of adhesive properties, the ability to form cements, the property of forming hard and insoluble masses akin to opal, combinations with pigments and colors of decorative value in the form of paints, glazes and enamels, the phenomenon of intumescence by which masses of value for thermal insulation and sound absorption may be made; finally, a brief consideration of the functions of soluble silicates as cleaners may not be out of place.
Silicate of Soda in the Building Industry JAMES G. VAIL
Philadelphia Quartz Company, Philadelphia, Pa.
The subject is discussed under the general headings of adhesives, cements, gels, films, intumescent products, and cleansers. Adhesive uses include wall board manufacture, bonding fibers, and water-resistant mixtures of casein and blood albumin. Films are used for fireproofing fabrics and structural timbers. Refractory cements, acid-resisting settings, welding rod coatings, and plastic masses for decorative panels are made with silicate of soda. Porous subsoil is consolidated by interaction of silicate and precipitants such as calcium chloride. Weather-resistant paints for glass, stone, etc., and permanent colors for roofing granules are prepared in a silicate vehicle. Anhydrous silicates are used in ceramic glazes and acid-resistant enamels. Thermal insulators are made by rapidly heating partially dehydrated silicates. Sodium meta- and sesquisilicates, alone or modified by soap or rosin, are efficient cleansers of concrete and metal.
UASTITATIVELY, silica is the most important compound in the architecture of Nature. This may also be true of structures raised by men, for silica is the major constituent of granite, slate, concrete, brick, and ceramic wares. Despite its slight solubility in mater, important rock masses and many minerals owe their present form to the workings of silica in solution. It is, then, natural to ask what part solutions of silica can play in the art of selecting and assembling materials to make buildings for human use. Time on a vast scale is required to petrify wood or develop large crystals of quartz from the dilute silica solutions which occur naturally. Chemists work with stronger solutions (alkaline silicates) which can be made to perform a t rates commensurate with our habitual haste. The uses of soluble silicates in this art might be considered in groups related to structural parts of buildings, such as foundations, walls, roofs, conduits, etc., but from the point of view of their chemical significance, it appears better to consider the functions which they can perform and some of the specific instances in which the peculiar characteristics of 888
Adhesive Uses One of the most widespread industrial applications of silicate solutions is for the purpose of combining fiber board of flat laminated or corrugated construction suitable for shipping containers. For this purpose colloidal silicates-that is, those in which silica greatly predominates over soda in the composition-are chosen. Sirupy liquids containing 3.3 parts silica to 1 part sodium oxide thicken rapidly with the removal of relatively small quantities of water. The characteristic curve shows a slow rise up to the region of 100 to 200 centipoises and then a much more rapid increase as water is removed. In the steep part of the curve the difference between a liquid and a solid, superficially considered, may represent a loss of as little as 1 per cent of water. Thus a thin film of silicate solution applied upon an absorbent paper surface gives rapid adhesion and provides a bond much stronger than the substance of the paper. This procedure has been extensively used in the manufacture of laminated wall boards made from vegetable fibers of various types. The technic is varied to suit the mechanical conditions of the combining machines. Such factors as the rate of set, the depth of penetration, the stiffness, and the solubility of the bond can be adjusted by regulation of the ratio between silica and alkali in the silicate, by the viscosity of the silicate as a function of concentration, or by the addition of mineral materials in finely divided condition (for example, see citation La). The choice . , of minerals, inert or r e a c t i v e , affects the ultimate solubility of the bond, and the amount of adhesive employed has much to do with t h e s t i f f n e s s attained. F o u r - p 1y 100-point board m a d e from wood p u l p a n d silicate bond has long been a s t a n d a r d type of wall board. Amuch-used form of w a l l board cons i s t s of s m o o t h wooden laths laid close together and covered on b o t h sides with a heavy layer of water-resistant paper (43). The laths are s e t i n a cement composed of silicate of soda and c a1 c i u m carbonate Courtesy, Tennessee Copper C o m p a n y ( f o r e x a m p l e , see FIGURE 1. GAY-LUSSAC TOWER BUILT c i t a t i o n 46), and the final protection WITH SODIUM SILICATE CEXENT
agaiiist vater is impartcd by treating the assembled board with solotions of waxes or resinous materials in suitable organic solvents. Another wsll hoard consists of multiple
cuuiter,,. Pennr,,fin"in sol, cornparty
Fsouns 2. Acru-ltr
ISTING C E M E N T T A N K OF' SODA AND SET RY IN1.ERN.U.t
