Abstract: The invention provides low viscosity iodinated aryl compounds, useful as X-ray contrast agents, of formula I ##STR1## (wherein n is 0 or 1, and where n is 1 each C.sub.6 R.sub.5 moeity may be the same or different; each group R is a hydrogen atom, an iodine atom or a hydrophilic moiety M or M.sub.1, two or three non-adjacent R groups in each C.sub.6 R.sub.5 moiety being iodine and at least one, and preferably two or three, R groups in each C.sub.6 R.sub.5 moiety being M or M.sub.1 moieties; X denotes a bond or a group providing a 1 to 7 atom chain linking two C.sub.6 R.sub.5 moieties or, where n is 0, X denotes a group R; each M independently is a non-ionic hydrophilic moiety; and each M.sub.1 independently represents a C.sub.1-4 alkyl group substituted by at least one hydroxyl group and optionally linked to the phenyl ring via a carbonyl, sulphone or sulphoxide group, at least one R group being an M.sub.1 moiety; with the proviso that where n is zero either at least one M.sub.

Abstract: The invention provides iodinated bis phenyl compounds, useful as X-ray contrast agents, of formula (I) (wherein each C.sub.6 R.sub.5 moiety may be the same or different; each denotes a hydrogen or iodine atom or a group M, two or three non-adjacent R groups on each C.sub.6 R.sub.5 moiety denoting iodine atoms and one, two or three R groups on each C.sub.6 R.sub.5 moiety denoting M groups; X denotes a group providing a 1, 2 or 3 atom chain linking the two C.sub.6 R.sub.5 groups, preferably where X is or contains in the bridging chain a carbonyloxy group each C.sub.6 R.sub.5 group being a triodophenyl group or a group in which each R is other than hydrogen; and each M is independently a non-ionic hydrophilic moiety, M preferably being a non-ionic hydrophilic moiety comprising a monohydroxy- or polyhydroxy-alkyl group) and isomers, especially stereoisomers and rotamers, thereof.

Abstract: In a subterranean drilling operation, a drill stem and drill bit are advanced downwardly while conducting compressed air downwardly through the drill stem. A minor part of the air flow is discharged from the drill bit downwardly against the sensible overburden, and a major part of the air flow is discharged upwardly through passages in the drill stem. A casing is disposed around the drill stem and advanced therewith so that the sensible overburden is shielded from the air discharged from the upwardly directed passages. The upwardly directed passages contain removable inserts which can be exchanged for different inserts in order to vary the amount of air discharged from the upwardly directed passages, and thereby vary the amount of air discharged downwardly from the drill bit against the overburden. In that way, the amount of air acting against the overburden can be adapted to the type of material in the overburden in order to control the amount of disruption to the overburden.