Abstract: The invention relates to a grinding wheel for machining metal circular-saw blades at relatively high rotational speeds, which have machining areas which contain in particular hard materials, such as for example diamond or cubic boron nitride. The grinding wheels according to the invention are intended in particular to improve the centring at relatively high rotational speeds, and consequently to prevent true running problems as far as possible. The base body of the grinding wheel is of contoured design, at least on one side, in the radially outer area of a tool-mounting bore, and at least one centring element can be designed to engage in a formfitting manner in the correspondingly designed contours, so that the grinding wheel and a centring element on a tool spindle of a grinding machine are held together in a force-fitting manner.

Abstract: Production of nitrilotriacetonitrile by reacting a salt of ammonia and a non-oxidizing acids with formaldehyde and hydrogen cyanide in an aqueous acid phase, at elevated temperature, completing the reaction and separating the reaction mixture into firstly crystalline nitrilotriacetonitrile and secondly an aqueous acid phase as the mother liquor. More particularly, a product obtained by primary reaction of an aqueous ammonium salt solution with an aqueous formaldehyde solution, the ammonium salt and formaldehyde being used in a ratio larger than 1:6, is reacted with a stoichiometric proportion of an aqueous hydrogen cyanide solution, the said stoichiometric proportion being based on the formaldehyde concentration of the primary reaction product.

Abstract: Production of halogen-containing tertiary phosphine oxides of the general formula I ##EQU1## in which the substituents R.sub.1, R.sub.2 and R.sub.3, being identical or different, stand for an alkyl, alkenyl, aryl or aralkyl radical, at least one of those radicals containing at least one aliphatically combined halogen atom. The compounds are made by reacting one or more compounds of the general formula II ##EQU2## in which R.sub.4, R.sub.5 and R.sub.6, being identical or different, stand for an alkyl, alkenyl, aryl or aralkyl radical, at least one of those R.sub.4, R.sub.5 and R.sub.6 radicals containing an aliphatically combined hydroxyl group, with at least equivalent proportions, based on the number of hydroxyl groups, of gaseous hydrogen halide with agitation, if desired, at temperatures within the range about 100.degree. and 300.degree.