460 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS TEST PRODUCTS Three generalised types of formula have been chosen and will be well known to the formulators of dentifrices. 1. Dicalcium phosphate dihydrate (DCP) type Dicalcium phosphate dihydrate 40.0 Precipitated calcium carbonate 5.0 Glycerine 20.0 Sodium lauryl sulphate 1.5-2.5 Thickener 0.5-2.0 Saccharin and flavour q.s. Water to 100 pH =7.8 2. Chalk type Precipitated calcium carbonate 45.0 Glycerine 20.0 Sodium lauryl sulphate 1.5 Thickener 0.5-2.0 Saccharin and flavour q.s. Water to 100 pH=10.0 3. Fluoride type Insoluble sodium n,etaphosphate 28.0 Precipitated hydrated silica 12.0 Glycerine 30.0 Stannous fluoride or monofluorophosphate Sodium lauryl sulphate Polyethylene glycol 1 500 Thickener Saccharin and flavour Water pH=4.5 0.4 or 0.8 1.5 2.0 0.5-2.0 to 100 PROCESSING METHODS The products have all been made on the 3 kg scale using Lang* stainless *Lang London Ltd., Southall Lane, Hounslow, Middx.

SYNTHETIC HYDROCOLLOIDS AND DENTIFRICES 461 steel vacuum mixers at a stirrer speed of 60 rev min- 1. Some of these products have also been made on other types of mixer in batch sizes up to 1 500 kg. The products made on the 3 kg scale are sufficiently like those made on the larger scale to permit the assumption that results from the laboratory batches will be similar to those which would be obtained in the factories. The hydrocolloid is usually added to the mixer as a powder, either to be dispersed in glycerine already in the mixer, prior to addition of water, or predispersed by dry mixing with polishing agent. In the case of those hydrocolloids which proved difficult to hydrate in aqueous glycerine, a preformed mucilage in water was prepared, although this method would be awkward to use in production. It is usually not necessary to apply heat to the mixer. TEST METHODS The properties of the toothpaste in which the hydrocolloid plays an important part are: consistency, texture, separation of liquid, colour, taste, foaming, dispersibility in the mouth and rinsibility. Consistency is measured using the cohesion tester*, an inexpensive, simple yet reliable instrument which measures the force required to pull apart a standard volume of toothpaste between two plates of standard area. The results (in g cohesion) give a good measure of changes in consistency of a given product, which correlate well with data collected using the Brookfield RVT with helipath stand at low shear rates. What is being measured is a function of 'viscosity' and 'pseudoplasticity' in the broadest meaning of those terms. Texture, separation, colour and flavour are judged by inspection and taste as comparison with standards. Dispersibility can be estimated by timing the disappearance of a ribbon of the toothpaste from a metal gauze trough being moved through water at a standard rate. Foam quality and quantity is measured by instruments and judged subjectively. THE EFFECT OF THE HYDROCOLLOID ON PRODUCT ATTRIBUTES The important consumer attributes controlled by the thickener are: (a) Rate of dispersion in the mouth (b) Rinsibility from the brush (c) The volume of foam produced *Longford Tool Ltd., Hampton Hill, Middx.