504 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table II WET Cake Moisture (WCM) Versus Structure Index (SI) % WCM 8O 81 82 83 84 85 Sl 400.0 426.3 455.5 488.2 525.0 566.7 dium prior to the acidulation. Figure 6 shows how the silica structure increases as the fraction of the theoretical silicate in the reaction medium increases. D. ELECTRON PHOTOMICROGRAPHS OF CONTROLLED STRUCTUKE SILICAS The electron photomicrographs of VHS (very high structure) and HS (high structure) silicas are shown in Figure 7. The comparative photomicrographs of MS (medium structure) and LS (low structure) silicas are shown in Figure 8. In Table III we have compared the particle size of the VHS to LS silicas. Examination of Table III clearly points to the fact that the primary particle size increases as the silica structure level decreases. Thus the control of particle size via controlling the silica structure provides an important tool for producing silicas for diverse specialty and cosmetic applications. 84 • 80 _• 75 • 70 •. 65 60 I I I I I I I ' ' 0 10 20 30 40 50 60 70 80 90 Percent Theoretical Silicate Figure 6. Method of controlling the silica structure

PROPERTIES AND STRUCTURE OF SILICAS 505 VH• •E½IPITATED SILICA •,•OX Figure 7. Electron photomicrographs of VHS and HS silicas I•A•OX Figure 8. Electron photomicrographs of MS and LS silicas