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tent, entirely satisfactory results in this respect being secured with an addition in any case of not more than one-half 'of 1 per cent of gypsum or plaster of Paris. Repeated tests show that ground clinker to which no re- tarder has been added and with a flash set, is given a reliable initial set of one hour, to one hour and ten min- utes, by addition of not over one-half 'of 1 per cent of gypsum with the waterproofing compound, 5. The results of numerous com- parative tests, with pliin cement and the same to which the process has been applied, show that, co far.as 1e- gards the tensile strength, constancy of volume and specific gravity, the waterproof cement compares favora- bly with the plain. The strength of the waterproof cement in all mixtures and for all lengths of time is fully equal to that of the corres- ponding plain cement. In the con- stancy of volume tests the parts made with waterproof cement remain firm and hard and show no signs of crack- Ing, distortion or disintegration what- ever, As yet no compression tests have been made. 6. Organic substances likely to un- "TAE Marine REVIEW ' . dergo any change or decomposition are not used, and the inorganic miner- al substances used are in such stable condition as to. jnsure that "no de- terioriation is likely to take place in the concrete due to their presence. 7. The requirement that the whole amount of ingredients used for water- proofing the cement should be so small that the total foreign matter in the cement, when put upon the mar- ket for tise, will not exceed the best standard requirements, severe as it is for waterproofing cement, is fully satisfied under this process. An ad- dition of not more than 2% per cent is needed, of the total ingredients, to produce the. required waterproofing, leaving one-half of 1 per cent for the addition of gypsum to complete the retarding of the initial set, (which is amply sufficient) before reaching the limit of 3 per cent total foreign mat- ter at present required. 8. The requirement that the process in all its operations and conditions should be free from complex manipu- lations and narrow limitations is fully met. Indeed, simplicity throughout is one of the principal characteristics of this process. Besides providing the 25 proper materials in suitable propor- tions, and a very simple treatment applied. to these as a whole, it is only necessary to secure thorough and intimate mixture with the cement, which is done by machinery, of course, and in a reliable way. There is, there- fore, every assurance that, in the ap- plication of the process, tne results: will be uniform and reliable. 9. It will be evident from what has been said of the process under 8 that little if anything in the way of ma- chinery would be needed in addition to what is found in the cement mills as they are 'at present constructed and operated.' The process could doubtless be applied at any existing plant in operation, without causing an hour's delay in the regular work, and with but a minimum expense in- curred for any additional facilities that may be required. 10. The requirement as to the' ad- ditional cost of the waterproofing treatment is very satisfactorily met. In a separate special report later on will be given full details as to the cost of applying the process. It will be sufficient at this time to state, (Continued on page 33.)