Introduction The work on the comparative tests of the effectiveness of coolants has continued. A wide range of soluble type coolants and straight oil coolants have been evaluated. The results of these tests are presented in a similar manner to that used in Progress Report Nos. 1 and 2, as Appendix A to Progress Report No. 2. From communications and inquiries in reference to the progress reports it may be that the clarity of the results could be improved to this end, more detailed attention to this is here included. Explanation of test results sheet headings. The Test Numbers, Wheel Type (specification Coolant, are all self explanatory. Grinding conditions This has been fully included in the progress reports, it is as follows: Table speed constant at 65 feet per minute Depth of cut constant at 0.001 ins. Gross feed constant at 0.042 ins. per table stroke Grinding wheel diameter maximum 7 ins. minimum 63/4 ins. Grinding wheel width 0.75 ins. constant. The grinding wheel specification and coolant are the variables, other conditions will be varied when initial testing is completed. The surface area ground. This heading means the area of surface ground under the standard conditions. per redress of the grinding wheel. All tests which achieve 75% of the previous test are repeated twice more. All products which achieve good results will be retested, and full calculations will be made. Full details and copies of results of any test are available on request. Surface finish The surface finish produced at each test is measured on the Taylor Hobson Talisurf. CLA is recorded, no trace record is made. This will be done when the most efficient products are retested. Where necessary brief remarks on a performance are included. These will be expanded and presented in greater detail when the final tests are made.