DEVELOPMENT OF A DETERGENT TEST 417 Figure A represents the data of the previous table. The plates in B were from a canteen after use for a meal of pies, potatoes, gravy. The hard water of C was prepared by adding 1,140 p.p.m. CaCI• and 710 p.p.m. MgCI• to distilled water. CONCLUSION The relationship between the concentration of a detergent solution and the number of plates washed is not a simple one, but shows a marked change in characteristics below what is identified as the critical micelie concentration. For a full evaluation of any detergent, therefore, it is necessary for a range of concentrations to be studied, and tests on different materials made at a single arbitrary concentration, particularly if this is in the critical region of about 0.025 per cent active matter, are liable to give misleading results. The effect of different quantities of soil on the plates is also complex. The fat/flour soil previously used shows an increase of about 40 per cent in the number of plates when only half as much soil is used, but an egg/fat soil shows roughly a two-fold increase, whereas a simple fat, most surprisingly, gives results nearly independent of the amount of fat on each plate. W. B. Smith, 'A. Taylor, J.S.C.C., ¾I, 96 (1955). Idem. 235.. Lloyd E. Weeks, Jay C. Harris, Earl L. Brown, J.A. Oil Chemists S., $1, 254 (1954). Clifford Pugh, Applied Statistics, 2, 172 (1953). Louis E. Wells, Soap • Chemical Specialties, $1, 54 (1955). SOCIETY OF COSMETIC CHEMISTS OF GREAT BRITAIN COSMETIC COURSE. 2nd YEAR EXAMINATION, 1956 This examination was held at Acton Technical College on Friday, June 22nd, 1956, one two-hour paper being set as follows: Answer Five Questions 1. Describe the difference between the sodium soaps made from (a) Coco- nut Oil and (b) Ground Nut Oil. 2. What are the principal criteria of rancidity of a vegetable oil ? 3. Describe how you would estimate traces of iron in a sample of soap. 4. What do you understand by the term Solubility Product ? Illustrate your answer by reference to a solution of Sodium Chloride and explain

418 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS the difference between the addition of ammonia to (a) a solution of Zinc Chloride, and to (b) a solution of Zinc Chloride and Ammonium Chloride. 5. Define the term pH. Calculate the pH of (a) 0-002 N HC1, (b) 0.002 N NaOH. Describe the effect on (a) and (b) of the addition of respec- tively an equal volume of (i) 0.02 N CH•COONa, (ii) 0.02 N NH4C1 with respect to the hydrogen ion concentration before and after the additions (log•02 is 0.3010). 6. Describe the preparation of high-grade Carnauba Wax from natural sources and describe the Laboratory examination of the product. ß 7. Outline the gravimetric analysis of a sample of Talc. 8. Briefly describe th• Laboratory examination of a sample of Zinc Oxide with reference to Lead content and Arsenic content. EXAMINER'S REPORT Questions 1 and 2 were generally well answered, but in question 3 most candidates omitted too many points of detail in the analytical procedure. Question 4 was quite well answered most students showed that they had understood the qualitative application of the notion of Solubility Product. Question 5 was not well done some candidates were unable to calculate the hydrogen ion concentration of 0-002 N NaOH. Question 6 was generally well answered, nearly all answers including a satisfactory account of the extraction of the wax from the leaves. The question on gravimetric analysis of talc was not attempted by any candidate. Question 8, on the Laboratory examination of zinc oxide was well answered by some of the candidates, but otherwise the standard of answer was rather poor. It is commonly the case that in this examination the descriptive essay type of question is answered well. Most candidates are weak on Physical Chemistry and on Analytical procedure, and whenever possible they avoid questions requiring precise factual information. Their answers indicate a reluctance to concentrate on detail they have a desire to accept the study line of least resistance and to skate broadly over a subject. They must overcome this if they are to make good progress in the work on which they are engaged.