640 Beport on the " JVorldnr/ Dairy " at the Derby Shoio. 
tube (a), which terminates in a T-outlet near the bottom of a 
spherical vessel of about 10 inches in diameter, which, encased 
in a cast-iron casing (e), rotates at a very high velocity, viz. 
GOOO or 7000 revolutions per minute. An instantaneous separa- 
tion takes place. The heavier portion, which represents what 
we call skim-milk, is thrown to the outside of the vessel, and 
forced up a bent perforated pipe which communicates with the 
open space (c), whence the milk is delivered into the middle of 
two block-tin trays or covers, which are provided with an outlet- 
pipe. The rapidity with which the milk enters the centrifuge 
must be regulated according to the velocity with which it is 
driven ; the greater the speed the more rapid the separation. 
The cream remains near the centre, rises round the outside of 
the inlet-pipe, and delivers itself into the upper tin tray (d), 
where it is discharged through an outlet-pipe. The rotating 
vessel and shaft are of forged steel, in one piece, tested by a 
pressure of 250 atmospheres. The shaft rests upon a cork pad 
(a wooden cup is now used) inserted in the driving-spindle. In 
the event of the power being cut off by the breaking of the 
strap, or any other cause, the vessel will continue to rotate for 
a considerable time." 
It is generally thought that, as far as separation goes, this 
Laval machine, described above, is about perfect. In an experi- 
ment in 1879, the skim-milk from the machine was tested with- 
out a trace of butter being obtained, and several experiments 
mentioned in a note to Mr. Coleman's report (p. 707) serve to 
show that Laval's process will give a superior result on the 
average to the " ice method." Yet it has certain disadvantages 
which do not render it a favourite with some who have been in 
the habit of using it. The enormous speed required is one of 
these drawbacks. A rate of 5000 to 6000 revolutions per minute, 
Avhich is now said to be requisite (instead of 6000 to 7000 quoted 
by Mr. Courtney) is still a prodigious speed, and an accident to 
any part of the machine might lead to very unpleasant conse- 
quences. Moreover, it will only separate about 30 gallons of 
milk an hour. 
The principal objection to the improved Lefeldt machine is 
perhaps its heavy and cumbersome make. The thickness of 
cream can be regulated by opening or closing valves within the 
machine ; but for this purpose the very heavy cast-iron top must 
be lilted off by pulleys. Another objection is that if the belt 
slackens, the machine must be stopped, as no alteration can be 
made while it is in motion. The number of revolutions required 
by the Lefeldt is 2400 per minute, and the separation is exceed- 
ingly good. The action is of course centrifugal, and, so far, on 
the same principle as Laval's (of which, indeed, in its original 
form it was the forerunner), but it is very different in diameter 
