238 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS as also should be the blade if this is used to cut the surface of the sample. The penetrometer itself should be of robust construction and operated in a manner that will not transmit vibration or shock to the samples at the time of impact and contact between the cone and sample. The instru- ment shown here is the type usually met with but may vary slightly. The cone should be preferably of stainless steel or hardened steel, as this is less liable to damage than one made from brass or stainless with stainless or hardened steel tip. It is essential that the cone be fabricated to the exter- nal dimensions specified and that the total moving weight, that is the weight of the cone plus the plunger, shall be 150 gm. If a light cone is used, a weight must be attached to bring the total weight to 150 gin. The speci- fied dimensions of the cone may be obtained from the "Standard Methods for Testing Petroleum and Its Prod- ucts," I.P. 50/48. The release mecha- nism should be perfectly smooth in action and the cone and attached shaft should be free to drop on release with- out appreciable friction. With samples and penetrometer pre- pared, the tests should be carried out without loss of time and if possible in a room in which the temperature is maintained within reasonable limits. The penetrometer should be set on a level bench free from vibration and the instrument adjusted until the sample platform is level, using the level gauge mounted on the base of the instrument. Place the sample on the penetrometer table, adjust the upper assembly so that the tip of the cone is 1 •/= in. from the side of the rim of the container, the tip being sited just above the surface of the sample. If the sample should have a consistency greater than 200, only one test should be carried out with the cone tip sited centrally over the container. Adjust the bottom platform until the tip of the cone is just touching the surface of the sample (adjustment is simple if a light is placed behind the cone to throw the shadow of the tip on to the surface of the jelly when the correct adjust- ment is arrived at by making the tip of the cone coincident with the tip of

USE OF PENETROMETER WITH PETROLEUM JELLY 239 the shadow). A mirror is mounted on the penetrometer to facilitate posi- tioning of the cone tip on the surface of the sample. Adjust the measure- ment bar so that it rests on top of the plunger bar, set the scale to zero, and quickly but gently release the plunger, keeping the release catch depressed for five seconds by stop watch while the cone penetrates the jelly surface. At the end of five seconds, take your thumb from the release catch so that the cone is held, carefully adjust the measurement bar to rest on the top of the plunger bar, and record the penetration which is shown on the scale in units of 1/10 mm. Report to the nearest 0.1 ram. Withdraw the cone from the jelly by depressing the release catch and moving the plunger and cone upward, wiping the cone free from jelly with a clean cloth and ascer- taining that no jelly or cloth fibres are on the cone before making the next test. The total surface area of jelly disturbed has a diameter approximately equal to the depth of penetration and it is essential that, for every subse- quent test on the same sample, the tip of the cone shall not be placed nearer the edge of the previous depression than a distance equal to the penetration of the previous determination. The number of tests which can be carried out on a sample will depend upon the diameter of the container and the con- sistency of the sample. If conditions permit, it is advisable to carry out ten tests on each sample recording the mean penetration of the ten tests. Any three test results should not differ from the mean by more than the following amounts: (a) with consistencies less than 200 ....................... 1.$ (b) with consistencies greater than 200 .................... 3.0 and the reproducibility with different operators'should not be greater than (c) with consistencies less than 200 ....................... 7 (d) with consistencies greater than 200 .................... 11 To illustrate variations in consistency, there is given in the table below results from samples of straight petroleum jelly, together with their melting points, and also results in consistency with melting points of petroleum jelly which has been doctored with additions of 1, 5, and 10% of paraflqn wax. From this table you will observe that, although the melting points may be quite close, the consistency can vary considerably.