18. Maxibrite briquettes, manufactured by Maxibrite Limited at Llantrisant, Mid Glamorgan, which—
(a)comprise anthracite fines (as to approximately 99 per cent. of the total weight) and bitumen as binder (as to the remaining weight);
(b)were manufactured from those constituents by a process involving roll-pressing and heat treatment at between 270°C and 300°C;
(c)are cushion-shaped briquettes marked with the letter “M” and have an average weight of 35 grammes; and
(d)have a sulphur content of approximately 1 per cent. of the total weight.