-----------------------+-------+------------+-------------+----------- | | Size of |Weight of all|Per Cent by |Weight.| Largest | the Finer | Weight of Size of Grain. | Grams.| Particles. | Particles. | all Finer | |Millimeters.| Grams. | Particles. -----------------------+-------+------------+-------------+----------- Above 2.20 millimeters | 1.50 | .... | 74.00 | =100= .98-2.20 millimeters | 7.00 | =2.20= | 72.50 | =98= .46- .98 millimeters | 22.00 | =.98= | 65.50 | =89= .24- .46 millimeters | 20.20 | =.46= | 43.50 | =60= .13- .24 millimeters | 9.20 | =.24= | 23.30 | =32= .08- .13 millimeters | 3.81 | =.13= | 14.10 | =19= .04- .08 millimeters | 5.13 | =.08= | 10.29 | =14= .01- .04 millimeters | 3.75 | =.04= | 5.16 | =7= Loss on ignition | | | | (assumed to be less | | | | than .01 millimeter)| 1.41 | =.01= | 1.41 | =1.9= -----------------------+-------+------------+-------------+----------- By plotting the heavy-faced figures we find that 10 and 60 per cent are respectively finer than .055 and .46 millimeter, and we have effective size .055 millimeter and uniformity coefficient 8. * * * * * The effective size and uniformity coefficient calculated in this way have proved to be most useful in various calculations, particularly in estimating the friction between the sands and gravels and water. The remainder of the article in the Report of the Mass. State Board of Health is devoted to a discussion of these relations which were mentioned in Chapter III of this volume. APPENDIX IV. FILTER STATISTICS. STATISTICS OF OPERATION OF SAND FILTERS.