620 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS powder, vehicle and additive employed. The following ranges of deviation were encountered with the systems tested: A v. Error Std. Der. Replicates, one operator, same day 4- 0.2 to 4- 0.3 4- 0.3 to 4- 0.7 Replicates, two operators, different days 4- 0.7 to 4- 1.2 4-0.9 to 4- 1.6 The degree of precision which could be attained was limited by the sample size and the size of the burette. The burette delivered 0.02 ml per drop, a difference of 1 unit in the wet point for a 2 g sample. For more precise determinations, a larger sample size and/or a smaller burette should be used. Flow Point Equipment: 50 ml burette, graduated in 0.10 ml intervals. 100 ml disposable beakers, approximately 2•" x 2«". Spatula with stainless steel blade, 4" x .•". Procedure: Weigh 20 4- 0.1 g of powder into the beaker. Weigh the additive on top of the powder. Incorporate the additive into the powder by rubbing the mixture against the sides of the beaker with the spatula. Add the vehicle from the burette, rapidly at first, then dropwise as the end point is approached. Mix thoroughly with the spatula after each addition of the vehicle. The end point is reached when just enough vehicle has been added so that the mixture flows in a uniform stream from the spatula (Figs. 3 and 4). Record the exact volume of vehicle added. Calculation: Multiply the ml of vehicle added by 5 to convert to the Flow Point expressed as ml/100 g. Precision: The sharpness of the end point varied slightly depending on the powder, vehicle and additive employed. The following ranges of deviation were encountered with the systems tested: Replicates, one operator, same day Replicates, two operators, different days A v. Error Std. Dev. 4- 1.0 to 4- 4.8 4- 1.4 to 4- 6.8 4- 2.9 to 4- 3.• 4- 4.1 to 4- 4.6

Figure 1 Titanium dioxide/mineral oil - just prior to wet point Figure • Titaniutn dioxide/mineral oil- at wet point .. Figure $ Titanium dioxide/mineral oil - just prior to flow point •ii • :' :::..s•: ......... i'.•!• ..... ½:. y i.,q: • .,,.-. • :72• •:::• '•'. .!' . .,- •::: :- .. ..-- . .::,.:: : Figure 4 Titanium dioxide/mineral oil - at flow point Facing page ( 20