MICHIGAN ACADEMY OF SCIENCE. 
85 
1 . 
2. 
Specific gravity 
1 . 1.38 
Calcium sulphate 
5.66 
2.3 
Calcium chloride 
1.0 
Magnesium sulphate 
Magnesium chloride 
2.015 
0.7 
Sodium chloride 
247.4 
265.7 
Total solids 
255.075 
269.7 
The above represents grams per kilogram. 
1. Filer and Sons, Filer City, Michigan. Analysis by W. and H. Heim, Saginaw, Michigan. Analysis 
furnished by Mr. E. G. Filer. 
2. Michigan Salt Co., Marine City, Michigan. Analysis by Robt. E. Devine, Detroit, Michigan. 
Analysis furnished by Mr. S. C. McLouth. 
As to the methods of manufacture, one, the open pan, employs direct 
beat, the others use steam, either live or exhaust. 
The open pan system may be thus briefly described. The pans, which 
are constructed of boiler plate, are about seventy feet long, twenty-five 
feet wide, and twelve inches deep, and have sloping sides to permit of 
the salt being raked onto the draining boards. The heat is furnished 
by a furnace placed at one end, the pan above being protected by a 
brick arch. The heated gases pass back under the pan to the chimney. 
In some cases, the chimney is placed beside the furnace, the gases, by 
means of a return flue, being made to traverse the length of the pan 
twice. 
The grainer consists of a rectangular vat, 100-1G0 feet long, 8-18 feet 
wide, and 22 inches deep, in which are placed steam pipes. The salt 
when formed is removed either bv hand with shovels or bv automatic 
t/ 
rakers. 
The vacuum pan consists of a vertical steel cylinder tapering at both 
ends, in the middle of which is a steam belt, through which the brine 
tubes pass, with a large tube in the center. A partial vacuum is main- 
tained in the pan so that the boiling point of the brine is considerably 
lowered. If the pan is run “single effect,” the steam formed by the 
evaporation of the brine is taken care of by a condenser. On the other 
hand, when two or more pans are run in “multiple effect” the steam 
formed in the first pan is conducted to the belt of the second pan on 
which a greater vacuum is carried and is used to furnish the heat for 
the second pan. The “triple effect” pan is in successful operation at a 
number of Michigan plants, and in New York state a “quadruple effect” 
is being operated. The salt, as it forms, drops to the bottom of the pan 
and is removed by a bucket elevator. 
With respect to the Alsberger system, I shall not go into details 
but merely state that the principle involved is that of superheating the 
brine under pressure and then running it into pans in which the de- 
position of the salt takes place without the further addition of heat. 
Revolving rakers scrape the salt into a well from the bottom of which 
it is drawn off into a centrifuge in the form of a paste and separated 
from the water. 
In the manufacture of table salt, the common salt is dried by passing 
it through a rotary kiln. The dried product is then separated into the 
