18 JACK PINE AND HEMLOCK FOR MECHANICAL PULP. 



wood a high-grade pulp will be produced, providing the grit of the 

 stone is suitable, irrespective of the style of the burr and within 

 reasonable limits of the pressure used. It is not impossible to con- 

 ceive of an artificial stone which could be used continually without 

 burring, which would clear itself without having depressions or 

 ridges, and which would have the correct size and kind of grit to give 

 the maximum production and best quality. 



TEMPERATURE. 



The temperature of grinding, it is said, has much to do with the 

 quality and quantity of pulp obtained, and many manufacturers 

 insist that it is impossible to secure a tough, strong fiber with anything 

 but the hot grinding process. It was noted in the experiments that 

 the rate of production was not nearly as great at a low temperature 

 as it was after a high one was reached. However, it was impossible 

 to detect microscopically any difference in the fibers themselves. As 

 has been said, the only observations made on cold grinding were 

 while the stone was warming up, and on this account it is impossible 

 to say definitely what particular advantages or disadvantages, if any, 

 lie in the hot grinding process. 



UNDETERMINED FACTORS. 



Since the experimental work on hemlock, jack pine, and spruce 

 was started a number of factors which more or less influence the 

 quality and the rate of production of pulp have made themselves 

 evident. These are the rate of growth of the wood, moisture content 

 of the wood, size of wood ground, temperature of grinding, the thick- 

 ness of stock in the grinder pit, and the grit of the pulp stone, the 

 last undoubtedly being the most important. All of these variables 

 will be studied in future experiments, though the grit of the pulp 

 stone is the one which will probably receive the greatest attention. 

 It is doubtful whether this very important item in the production of 

 ground wood has been given sufficient consideration by manufacturers. 



MICROSCOPIC COMPARISON OF EXPERIMENTAL PULPS AND 

 COMMERCIAL STANDARDS. 



STANDARD PULPS. 



Since it was necessary to have some means of comparing the 

 experimental pulps produced with commercial products, portions of 

 the samples obtained from manufacturers were photographed, in an 

 endeavor to classify the fibers according to their quality. It was 

 found that there is a more or less regular grading of the material 

 from long, fine fiber to pulp which is almost a powder. It is probable 



