meus tested n t low stresses (5-100 g./cni.3) nud thc followiiig features observe+ Thc variation of nppnrcnt viscosity -qc +?D ovcr thc raiigc of bitunions tcstcd ITDS vcry great, tho. c-*cut of rariatiou at 28' C.
being from loa poiscs to 10l2 poiscs. Tho viscosity was found to decrensc with incrensc of temperntiire. The static elnsticity Eu wns not found t o mry,to any great cxtciit, thc ratio of the innsimuni to the minimum .value observed being 10. The value of Bn dccrenscd only sliglitly with iiicrcnsc of temperature. E,1 .could only be mensured for threc bituinens nnd its \due wns found to bc nt lcnst 100 times that of &. The vnluc of for stcnm-distilled bitunicn wns about 20 times that for blown bitumen. As tho viscosity ratio betwccii tlicse bituinciis is of tlic order of 2-3 it appenrs that the diffcreucc bctwecii thc two types is largely dcpciidciit on thc \due of EA. E,\ ans found to decrense rapidly with iiicrense of tcmperaturc. ' q D wns fouiid to be grentet than -/id; tIic valuc of .qD/qc is, however, much grcntcr for blo\vn bituiiiciis tliaii for stenn~-distillcd bituniciis of tho snmc class. This will nlso cont,ributc to the dill'erciicc in mcchniiical propertics of the two:typcs siiicc tho iiiitinl rate of dcforiiiation uiidcr a loud P is froin equntioii (G) {P/3(-qc + q~)} X
(1 +q~//ic). , The viscosityqc +;qD of Iilown bituiiitwi is gericrnlly less tlinii tlint of stcniu-distille(1 bititincus of tlic snnie type, so tlint tho iiiitinl rate of deformation wiII bc gicntcr for blown bitumens.
Tho dccrensc of viscosity with iiicrensc of stress is very innrkcd, fnlliiig froni nbont 10" poiscs ut 28 g./cni.? to iiboiit los poises a t 10,ooO g./ci~i.~ (20 Ib./ctn.?) iii tlic cnsc of bitinnci,2 nt.8' G. Thc constniits obtriined n t Ion strcsscs do not tliqreforc intlicatc tho