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The Babcock Milk-tester


It is not sufficient for a farmer or a dairyman to know how much milk

each of his cows yields. He should also know how rich the milk is in

butter-fat. Wide-awake makers of butter and cheese now buy milk, not by

the pound or by the gallon, but by the amount of butter-fat contained in

each pound or gallon of milk. A gallon of milk containing four and a

half per cent of fat will consequently be worth more than a gallon

taining only three per cent of fat. So it may happen that a cow

giving only two gallons of milk may pay a butter-maker more than a cow

giving three gallons of milk. Of course it is easy to weigh or measure

the quantity of milk given by a cow, and most milkers keep this record;

but until recent years there was no way to find out the amount of fat in

a cow's milk except by a slow and costly chemical test. Dairymen could

only guess at the richness of milk.

In 1890 Dr. S. M. Babcock of the Wisconsin Experiment Station invented a

wonderful little machine that quickly and cheaply measures the fat in

milk. Few machines are more useful. So desirous was Dr. Babcock of

helping the farmers that he would not add to the cost of his machine by

taking out a patent on his invention. His only reward has been the fame

won by the invention of the machine, which bears his name. This most

useful tester is now made in various sizes so that every handler of milk

may buy one suited to his needs and do his own testing at very little


The operation of the machine is very simple. Suppose that the members of

the class studying this book have been asked to take a Babcock machine

and test the milk of a small herd of cows. They can readily do so by

following these directions:

While the milk is still warm from the first cow to be tested, mix it

thoroughly by pouring it at least four times from one vessel to another.

A few ounces of this mixed milk is then taken for a sample, and

carefully marked with the name of the cow. A number is also put on the

sample, and both the cow's name and the number entered in a notebook. A

small glass instrument, called a pipette, comes with each machine. Put

one end of the pipette into the milk sample and the other end into the

mouth. Suck milk into the pipette until the milk comes up to the mark on

the side of the pipette. As soon as the mark is reached, withdraw the

pipette from the mouth and quickly press the forefinger on the mouth

end. The pressure of the finger will keep the milk from running out.

Then put the lower end of the pipette into one of the small long-necked

bottles of the machine, and, lifting the finger, allow the milk to flow

gently into the bottle. Expel all the milk by blowing through the


The next step is to add a strong, biting acid known as sulphuric acid to

the test-bottle into which you have just put the milk. A glass marked to

show just how much acid to use also comes with the machine. Fill this

glass measure to the mark. Then pour the acid carefully into the

test-bottle. Be sure not to drop any of the acid on your hands or your

clothes. As the acid is heavier than the milk, it will sink to the

bottom of the bottle. With a gentle whirling motion, shake the bottle

until the two fluids are thoroughly mixed. The mixture will turn a dark

brown and become very warm.

Now fill the other bottles in the same way with samples drawn from

different cows. Treat all the samples precisely as you did the first. Do

not forget to put on each sample the name of the cow giving the milk and

on each test-bottle a number corresponding to the name of the cow.

You are now ready to put the test-bottles in the sockets of the machine.

Arrange the bottles in the sockets so that the whirling frame of the

machine will be balanced. Fit the cover on the machine and turn the

handle slowly. Gradually gain in speed until the machine is whirled

rapidly. Continue the turning for about seven minutes at the speed

stated in the book of directions.

After this first turning is finished, pour enough hot water into each

test-bottle to cause the fat to rise to the neck of the bottle. Re-cover

the machine and turn for one minute. Again add hot water to each bottle

until all the fat rises into the neck of the bottle and again turn one


There remains now only the reading of the record. On the neck of each

bottle there are marks to measure the amount of fat. If the fat inside

the tube reaches only from the lowest mark to the second mark, then

there is only one per cent of fat in this cow's milk. This means that

the owner of the cow gets only one pound of butter-fat from each

hundred pounds of her milk. Such a cow would not be at all profitable to

a butter-seller. If the fat in another test-bottle reaches from the

lowest mark to the fourth mark, then you put in your record-book that

this cow's milk contains four per cent of butter-fat. This record shows

that the second cow's milk yields four pounds of fat to every hundred

pounds of milk. This cow is three times more valuable to a butter-maker

than the first cow. In the same way add one more per cent for each

higher mark reached by the fat. Four and one-half per cent is a good

record for a cow to make. Some cows yield as high as five or six per

cent but they do not generally keep up this record all the year.

The tester, acid, acid measure, test-bottle, and thermometer at bottom;

filling the pipette on right; adding the acid and measuring the fat at


The Babcock tester shows only the amount of pure butter-fat in the milk.

It does not tell the exact amount of finished butter which is made from

100 pounds of milk. This is because butter contains a few other things

in addition to pure butter-fat. Finished and salted butter weighs on an

average about one sixth more than the fat shown by the tester. Hence to

get the exact amount of butter in every 100 pounds of milk, you will

have to add one sixth to the record shown by the tester. Suppose, for

example, you took one sample from 600 pounds of milk and that your test

showed 4 per cent of fat in every 100 pounds of milk. Then, as you had

600 pounds of milk, you would have 24 pounds of butter-fat. This fat,

after it has been salted and after it has absorbed moisture as butter

does, will gain one sixth in weight. As one sixth of 24 is 4, this new 4

pounds must be added to the weight of the butter-fat. Hence the 600

pounds of milk would produce about 28 pounds of butter.


1. Find the number of pounds of butter in 1200 pounds of milk that

tests 3 per cent of butter-fat.

2. A cow yields 4800 pounds of milk in a year. Her milk tests 4 per

cent of butter-fat. Find the total amount of butter-fat she yields.

Find also the total amount of butter.

3. The milk of two cows was tested: one yielded in a year 6000

pounds of milk that tested 3 per cent of fat; the other yielded

5000 pounds that tested 4 per cent. Which cow yielded the more

butter-fat? What was the money value of the butter produced by each

if butter-fat is worth twenty-five cents a pound?