Paper read before the Bristol Section on October I I , 1934 INTRODUCTION JInxiy conflicting cliiiiiis nrc iiintle for tlic iiiittcriiils used in tlic surfncing of roads, nud it is prol)oscd to give considcrntioii t o tlie iiiost witlcly I I X C ~, vie. : iispli:ilt, bitumen, iiiid tnr niitl to indiciite tlic niiiiiiier i n wliicli t h y call be ciiiplopd to tllc h s t iid'iilitngC wlicii forniing :in intcgnil part, of tlic road surfncc Inycr, wliicli is superiniposctl 011 tlic foundittion. It. is proposcd to cscliidc, on tliis occnsion, ill1 rcfcrcriccs to their respective propcrtics wlicn iisctl rucrcly :is :I surfncc dressing. DEFINITIONS (COMMERCIAL) Bitto)ic)i is dcfincd ns " misturcs of niiturnl iintl pyrogcnous hydrocurbons, niid of tlicir nn~i-iiwt:illie tleriwt ires, wliicli riiiiy Lc giiscous, liquid, viscous, or solitl, Init m i s t be coiiiplctcly sulublc in CS,." This definition covcrs i i Inrgc Il~lill~JCr of diflcrciit substniiccs, hut only t,liosc occurring ~inturiilly in iissociiitioii with niiiicriil ninttcr or thosc ~vhicli cnn be iiiiiiiufiicturctl into iispliiilt can be inclutlctl uiitlcr tlie liecitliiig *' nsp1i;iltic I~itiiincn." .-Isp/ictOic Iitiiincii is tlcfiiicd ns *' iiiituriil or nnturiilly occurring IJitriincii or I~itriiiicii prep:ircd from iintiiriil Iiydrocnrl~oiis 11y distillittion, or osidiition, or criickiiig : solid or viscous conttiiniiig it low proportion of volntilc products : possessing c:li:irnctcristic :iggloiiier:ttiiig propcrtics niid ~i ~I ) ~t i i ~i t i ~i l l . ~ soluble in CS, . " Il'A 1II.E 1 . y'he ~J ~O ~J C I ~i t ! d 01 ~lU]Jlltlll rod* Val dc SL. Jeari Siciliiiti Triiwrs C~!TIIIIIII 8cyfiseI Ilitulticticontcnt. 1 0 * 4 ~o S-Uo/i 8 . 3 O ' to 4 * " O ' -/u *I.!% I{ccorerctl bit umen : l'etletriitioi~