The aliiminiin salts of the higher fat'ty acids find considerable use in t,he manufacture of paint.s, for thickening hydrocarbon oils (greases), and ns stabilizers for emulsions (13,20). Their nature and composition are, ho\vever, siuprisingly obscure. Corninercially they are made by an aqueous double decomposil ion process (13,20). The composition and thickening (often termed "gelling") pi'operties of the find product depend critically on a number of factors, siich as the pH and tempernture during the precipitat,ion, the speed of mising, the size of the particles formed, etc. One Trery important factor is the ma8nner nntl est8eiits of t81ie drying of the precipit#ute once it has been formed and \rashecl. In scienl ific in~estigat~ions of t,heir composition a non-aqueous double tleconiposit'ion react ion, such as that' Iiet'iveen an aluminum alkoside and rl. fatty acid, has much to i'ecommend it, as t,lie little-knonii influence of writer can be eliminated 01' conti-oiCerI.McBain and ,1IcClatchie (21), \\rho reacted aluininiun ethoside \\.it,h pnlmit ic acid, fount1 that not more ihan ti\co fatt'y acid groups coiild lie atltnclietl t,o each aliiminum :Itom, m t l they concluded th:Lt the tjrisoap does not, exist. In point, of fact, t'heir most reliable an:tlyais figures intlicnt8e 2% lower extent of react ion e\-en than t,\\,o fntt'y acid groups. Thliies of 5.2-5.4 per cent) A41,0a \yere found; nluminim etlioside \\.ith 13 fnttp acid groups replaced by pa1mit)ic acid coinresponds t,o 5.44 per cent AI?O3. AlcBain's co\yorliers ( 2 i ) have 1,eceiitly considered t,he qiiest'ion in greater detail. From a study using the aqueous pi*ecipit8ation met,hod t'hey conclridecl tlint bot'h the monolnurate and the dilanrate exist, ns tlefiii ite clirinical indivicliials and t'lie x-ray tlat'a are claimed t o support this T.ie\y.Eigenliei3ger and Eigenher~er-Bitt'i~er (11, 12), in n yery full esamiiintioll of l)otjh tlic nqiieous and noli-aqiieous precipitat'ion methods, conclutlecl t hat, in Iioth 1 Prcsciited at the Twciity-second Nntioiial Colloid Symposium, which WLS licit1 U I I C I C~ t h e nuspices of tjhe Division of Colloid Chemistry of the Biiierican Clielnicnl RocictJ, nt Cniiil)t~itlge, 1Inssnchuset ts, Julie 23-25, 194s.