REVIEWS 71 



The amount of combined SO,, total SOo being constant, total SO2 

 ratio combined to free SOo being constant ; temperature. 



The conclusions drawn are briefly as follows : 1 per cent combined 

 SO2 is the smallest amount possible with good results. Increasing 

 amounts of combined SO, seem to increase uniformity of cooking, but 

 decrease the speed. 



Five per cent total SO2 seems to be the lowest amount of total SO2 

 consistent with good results. The higher the SOg the easier the 

 bleaching of the pulp. The lower the temperature the more uniform 

 the cooking and the easier the bleaching. 



While data for only twenty cooks are given they represent the re- 

 sults of ten years' of pioneer work in the design and operation of 

 pulping apparatus on a semi-commercial scale, and the fact that this is 

 the first publication of investigating work on cooking by the sulphite 

 process, in which definite indications of a quantitative nature are given 

 reflects great credit to the author and the organization which he repre- 

 sents. It is hoped that the work will be continued and the effect of 

 the other cooking variables in this process, such as the ratio of mag- 

 nesium and calcium in the cooking acid, rate of gassing, etc., be deter- 

 mined and published for the benefit of the industry. 



S. D. W. 



Progress Report on IVood-Block Paving Experiments in Minne- 

 apolis. By C. H. Teesdale and J. D. MacLean. In Proceedings of the 

 fifteenth annual meeting of the American Wood Preservers' Associa- 

 tion. 1919. Pp. 124-133. 



This experimental piece of treated wood-block pavement was laid 

 in 1906 in the city of Minneapolis in co-operation with the Forest 

 Service and various lumber manufacturers and wood-preserving com- 

 panies. Full details of the experiment will be found in Forest 

 Service Circular No. 141. The first progress report was published in 

 1913 as F. S. Circular No. 194. A further discussion of the tests 

 appeared in the Municipal Journal, May G, 1915. 



The main purpose of the experiment was to determine the relative 

 merits of various species of wood for paving material. Study was 

 also made of the influence of certain variables, namely, heartwood and 

 sapwood, length of blocks, and angles of courses. 



In the early part of 1911, two sections of Douglas fir blocks were 

 relaid. In one spot, comprising an area of about 30 square feet, the 

 blocks were so badly worn that they were completely shattered into 

 small bits. This failure was attributed to the poor grade of material 



