actunlly flowiug through them ; this will lctrd to precipitntion of tllc bulk of the cnlciuni sulphnte present in supersnturnted solution. It liirs been observed thnt settled ningnesiir slurry, originrilly free from crystals of cnlciiuui sulphnte, heconies henvily contnminnted on standing in a settling and tliickcning t.nrik over IL period when the air and sen wnter tempcrnturc hnve cousidernbly decrensed. Tlic settled nnd thickened inngnesittm hydroxide is hcnted to 90" for several hours in order to lrid thc dewnt.ering process in the continuous vircuuni filters. As the solubility of mlciuni sirlphnte rises to n innximum n t 40' iriitl t~lierenftcr rnpiilly tlccrenscs, it is very prohnlde that nny supersiitiirirtion of the sea wnttr trssocintcd with the magnesium hydroxide will he destroyed iii the slurry henting tanks. This has been found to occur nnd to lend to ilicrwsetl contnminritiolr of the product arid nl6o to troul~lrsnn~e deposits of errlci~un sulphnte s d c in pipes niid filtrirtioii cquiplncnt.
The experinients tlrseriIwtI rcliitt! to the reuction between pure crtlciuiu cxide ;rnd seir witcr, bitt on the lirrge-sciile doloniitic or high-cnlcium lime rcilviiicd in slinft or rotnry kilns is used, riiitl it slioi~ld Iir noted thirt c:uIc*incition norni:illy lenils to coiitirminirtion of thv liinc: with sulpliiir frotii the fuel. The proportion prescnt ns sttlphetc. will contrihtv iri the. wtiiie wrry to the rtttninnient of snturntim iis t i n equivnlr~it. arriouiit. of' cirl(.iiiin sulphritc fornictl in the ruction. Jf tlie linie ifi c-iilciiictl in ii gns-fired kiln it is possible hy \vitshing the producer gus nornurlly used to reduce it,a sulphur eiintent, but this procedure liiirterinlly increirscs the fuel constimptiolt iind therefore the cost of the Iwoduct. its ail nlternntive to wnsliing thi: protlucer gas the iiniount of lime used in tlie renction mug lie rrtlucecl in order to ensure tllat tlip spent sen wvritcr docs not beconie supcrtinturnted. This resiilts iti ir lower yield of iiingnesiir and i n iiic!renaed costs of opcwtion H) t . h t ii coinpromivc is iisiially sought. COSULURlON 'I'hc solubility product [cir + +] . [SO,"] is exceeded if cirlciurn ccmipletely replnces nmgiresium in North Sea wnter, but enlciuni siilphntc is not inrnidiately prccipit.nted owing to the fornuition of rclittivcly stable supcrsnturated solutions. Tho limiting concentrntion of calcium ion wns fouud to be 96.0 mgm. cquivnlents per 1,OOO gin. wticn 72.6% of the totnl niugnesium ion hnd been precipitated. We wish to t.liunk the Ilirectors of thc British Pericliise Co. for pcrmissioli to pubhili t.hiN piper. Yiilliscr Works, Bnrtlcpool, Co. I)urharii. A C'omprclrcmivu Trt!ati..t! uii Iiiorguiiic mid Theorvtinil Chumistry, by