The sodium silicates in general use in the paper industry consist of chemical combinations of SiO and 2 Na O in ratios varying from about 1:1 to about 4:1. 2 They are available as aqueous solu-tions, anhydrous solids, and crystal-line hydrates depending upon their chemical composition and the use for which they are intended. These uses will influence the tests which are required. When the utility is based on their chemical nature, the essential deter-minations are the Na O and SiO content; when used 2 2 as an adhesive, their viscosity and gravity become important.