232 ANNUAL REPORT 
Campbell Mixer,—The Campbell machine consists of a horizontal 
circular pan revolving about a vertical axis and having a set of stationary 
plows fixed to a frame which can be raised or lowered into the pan. 
The pan carries the material against the plows and they throw the material 
back and forth in the pan as it revolves until the concrete is thoroughly 
mixed. A trap door in the bottom of the pan is then opened and the 
plows raised, while a scraping bar is lowered and the batch of concrete is 
scraped and dropped through the trap door into the transporting recep- 
tacle below. ‘There are two sets of plows, one right hand and the other 
left hand. 
“Time actually consumed in charging machine for one yard of con- 
crete, completing the mixture and dumping the machine ready for the 
next batch, three minutes and ten seconds.” Illustrations of the machine 
are given in figures 133 and 134. Specifications of size, weight and 
capacity are also appended. 
Cubical Mixers.—There is a variety of cubical mixers, prob- 
ably developed because the United States army officers at one time threw 
the weight of their commendations toward that form of mixer. This 
general form is supported so as to revolve upon a diagonal axis and thus 
throw the concrete mixture from one to the other of six different faces, 
each rapidly assuming a different angle to the horizontal and vertical 
planes as the cube revolves. One form of the cubical mixer is shown in 
figure 135. This is so arranged that it can be loaded at one end and 
discharged at the other, both operations taking place without stopping the 
machine’s rotation. 
Gravity Mixer.—Figures 136 and 137 show a simple gravity mixer 
which answers very well for some purposes. It consists of a funnel 
shaped receiving end attached to a box shaped chute having staggered 
rows of pins at frequent intervals along its length. It is also fitted with 
deflecting plates to throw the material from side to side as it descends 
through this chute, which is suspended at an angle of about 20 to 25 
degrees from the vertical. The box is made in sections easily joined 
together so that various lengths, from four to ten feet, may be used for 
different classes of work and surrounding conditions. There is some 
doubt as to the thoroughness of the mixing obtained, also as to the even 
tempering of the mixture with water. There is much rough concrete foun- 
dation work, however, where this simple form of mixer might be satis- 
factory. Limited space allows the description of but one of the many 
other forms of mixers. 
Dromedary Mixer. —The Dromedary mixer is a unique development 
of the two wheeled cart. The inventor evidently designed this to answer 
two purposes, first to utilize horse power to do his mixing, and second, to 
utilize for mixing, the power and time necessary to haul the material to 
