From the 1940s on, the Bay of Quinte was subjected to increased point-source phosphorus loading. This and other stresses (exploitation, fish species invasion, and perhaps climate fluctuation) altered the productivity of the ecosystem and community structure. In the late 1970s, point-source loading was greatly reduced. At the same time, walleye (Stizostedion vitreum vitreurn) produced the largest year class ever recorded and surged to abundance greater than those seen in the 1950s before its collapse. Also, the dominant invader white perch (Morone americana), which had flourished in the 1960s and 1970s, was almost eliminated by a low-temperature kill. Studies of the bay ecosystem before and after these events indicated that while nutrients and algae responded to changes in nutrient loadings, changes in secondary producers hinged on the changes in the fish community. Use of Borgmann's biomass size spectrum model provides a focus for the interpretation of nutrient- and predator-related changes in biomass distribution. Deviations of the biomass spectrum are interpreted. The biomass and production spectra are linked to both phosphorus concentrations, observed and predicted, and to fishery exploitation rates. The results suggest that while nutrients control the overall biomass of the ecosystem and the slope of the biomass spectrum, trophic interactions and perturbations (e.g. exploitation) determine the degree to which a smooth biomass spectrum is achieved.

Eight ring-ditches and several stretches of pit alignment have been excavated between 1981 and 1985, as part of the investigation of an extensive cropmark complex on a gravel terrace in the Upper Severn valley at Four Crosses, northern Powys. Excavation of the ring-ditches, which form part of a more scattered barrow cemetery, has revealed a long and complex pattern of development of barrow types and burial forms in the period between the Middle Neolithic and the Middle Bronze Age. This is compared with the recently published sequence from the neighbouring upland barrow cemetery at Trelystan, and subdivided into four hypothetical phases. There is evidence of activity in the vicinity of some of the sites in the Iron Age, Romano-British, and possibly the early post-Roman period.

July 15, 1Od2 ' CHEMISTRY AND INDUSTRY 000'werc nbIc to i1istingiiisIi four typcs of peptization or colloidnl dissolut~ion : (1) ndsorption pcptizntion (carbon and picric nciil) ; (2) dissolution pcptizntion (mctnl hyclrosidcs nnd ncitls) ; (3) pcptizntion through smelling (gelnt,in in wntcr) ; (4) spontnncous colloidnl tlissoliition (dycs nnil sonps in wit,cr, ccllulosc ncet.ntc in chloroform). Adsorptioniiiicl dissoliitioii-pcptizntioii arc chnrnctcrized hy n n optinirim for inccliiini nmounts of solid phase, which is not obsorvetl ns ii riilc in tlic rcmnining two metliods of dissolution, whore tho ciirve iisiinlly rises stenclily. Tlic pcptizrition of strinnic ncitl by liydrocliloric iiciil, zinc liytlrositlc by soiliiim Iiydrositle, nntl bismuth liyilrosidc by lactose or sucrose fiirnishcd results in nccorclance with thc solid-phase rule, but csceptions nppcrirctl in blic systems zinc hyyilroxidc-liytlrocliloric ncitl and zinc liydrositlc-ncetic ncid, in wlJcli cnscs tlic solubility is indcpcntlcnt of the iirnoiint of tlic solid phrisc. It, is ~~r011ril~Ic t l i n t piircly clicniicnl reaction is mriitily conccrnctl in tlic csccptioii:il cnscs, diilst tlic solid-plinsc rirle epplios to tlic systciiis in\~ol\~ing the opcrntion cliiclly of colloitl-clicmicn1 proccsscs.The rclat ions I)ctwcc!n colloicl:il soliil)ilit~y riiitl inolcciilnr solul~ility linvc bccn clisc~~sscd I J~ .Jcrniolenko,lz who lins cst.alilislict1 t,hc vnliditey of tho solid-pliiisc rille in tho dissolution of copper c:irl)onntc hy rimnioiiiii in t,lic prcscncc of niniiionirini cliloriclc.I hc s~velling of gels lins rilso bccn found to cscniplify thc solid-plinse rulc. Ostivnltl nntl Ktililcr*z ol).wrvetl that tlic relntivc sivclling of gelritin in m t e r frills ns tho rirtio of t,lic solid plinse to the liquid is increnscd. Thc spont:incous tlissoliition of gelritin in writer rilso iiicrcnscs ris tlic ;mount; of gclntin is increnscd. 'l'ho obscrvat,ion that3 tlic inflricnco of t h solid plinsc oil I)pth tlicse proccsscs is niiirkcilly less a t lower tcmpcriiturcs has consitlcrrrblc significnncc. hcoriling to Lloytl,'J the influciicc of tlic volume of liqiiitl on t h s\vclling of conimcrci:il gcliitiii is tlirc to tlm cliniigcs i n tlic rclative coi~ccnt~rntion of clectrolytcs ;tiid ilcgrndntion products of gclritin ~~rcscnt~ as in~piiritics. 'l'lic vnriation of the rlcgrce of s\vclling in sodiiiui hydroside solutions with the voliinic of tho solution is nttrildxd to hydrolytic decoinposition of tlic gcliitin. Wlicn piire gcltitin swclls ti12 CHEXISTHY AND LVDUSTRY Jitly 15, 1032