136 ANNUAL REPORT 
Magnesia. —Prof. N. W. Lord determines magnesia volumetrically 
by precipitating as magnesium ammonium phosphate, filtering, washing, 
treating with 1-10 normal sulphuric acid and titrating back with 1-10 
normal ammonia, using cochineal indicator. 
Ludlow and Harrop Method.—In order to illustrate actual labora- 
tory practice the methods employed at two cement works are given, the 
first one being used at the works of the National Portland Cement Com- 
pany, Durham, Canada, having been worked out by Mr. S. H. Ludlow, 
chief chemist, and Mr. Carl B. Harrop, assistant chemist. Mr. Ludlow 
has kindly sent the following account of the method: 
RAPID METHOD OF RUNNING PORTLAND CEMENT MIXTURES. 
The following methods of determining the amount of clay to be added to a given 
measured quantity of marl in the wet state to produce a correct slurry are based upon 
the relations existing between the weight and volume of a cubic yard and a cubic centi- 
meter of water. 
Re juired to find the number of pounds of clay to be added to a cu. yd. of marl of 
any composition or consistency. Take such a volume of the marl that the weight of the 
total solids in the volume taken, expressed in milligrams, will represent pounds per 
cu. yd. By a familiar course of reasoning, similar to that employed in establishing the 
assay ton, the following proportion may be deduced: 
Original volume : part taken :: mass represented : part of represented mass taken 
as unit in analysis. 
Let A = Original volume. 
Let B = Mass represented or one pound. 
Let 1 = Part of represented mass taken as a unit in analysis, or one mgm. 
Let X = Part of original volume taken or number of ce.required, so that each mgm. 
will equal pounds per cu. yd. 
Substituting— 
ite Gere Beat 
1 cu. yd. = 764500 cc. (or gram of water). 
1 lb. = 453593 mgm. 
Therefore, A = 764500 cc. 
B = 453593 mgm. 
Substituting and solving for X, 
764500 : X :: 453593 : 1 
Xe — I OSoncce 
Hence if 1.685 ec. of water (standard conditions) is taken, each mgm. equals 1 
; ound in the cu. yd. Obviously this will apply to any liquid of whatever density or to 
a homogeneous mixture of solids and liquids or a thoroughly agitated sample of marl in 
the semi-liquid state. 
Therefore, if 1.685 cc. of marl be evaporated to dryness, in a tared dish, and 
weighed, its weight expressed in miligrams equals the number of pounds of marl per 
cu. yd. The weight of marl in a given volume being known, the amount of clay to be 
added may be readily calculated from the composition of the marl and clay, and the 
desired composition of the slurry. 
Several applications of this principle may be made according to the uniformity of 
the marl, the system of mixing in the mill and the facilities for correction of slurry, 
should occasion Cemand. 
