MILE-TESTING.

Otago Witness, Issue 2471, 24 July 1901, Page 9

MILE-TESTING.

(W. M. Sixgleton, Dairy Instructor.)

Until the year 1850, when the factory sys- I tern of cheese manufacture developed, the { «\ibj€ct of milk-testing aad little attention. This new development, accompanied, a few years later, by a similar one in butter, made it necessary to have some method of testing milk, particularly as to its fat content. Since that time different chemists have endeavoured to give the public a test which would be accurate, simple, and cheap, but all tests devised seemed to come short in one Ox more points, until, in. 1890, Dr Babcock introduced his famous te,«t which has since given such universal satisfaction. Since the introduction of this test j large number of different gtyles of machines have bten placed on the market. In getting a machine- it is important to select one that is durable and will run smoothly whether loaded or empty. If you are selecting a turbine do not have the jet of steam striking near your bottles, and have a hole in the centre of the cover large enough to permit the proper circulation of air. See that the pockets are not easily detached, and that when the machine is running, the bottles canj assume a perfectly horizontal position and a perpendicular one when at rest. It is \-ery important to have the bottles properly graduated. They may be callibrated by using either mercury or water, or a still simpler method is to test one sample of milk- with the different bottles, and then discard those that are as much as one-tenth astray. The accuracy of a milk test depends principally on the sampling. Unless the operator gets a fair average sample he may just as well approximate the percentages, as to run the test through and get misleading results. In order to get a true sample the milk should be poured from one vessel to another. Howevei, when milk is drawn to a factory, the agitation it gets on the way and the subsequent pouring into ihe weigh-can -generally makes a thorough mixture. J

As a rule, in ordinary factory work the ounce dipper is sufficiently accurate, and is most convenient for taking composite samples. Each morning a sample of millTSe taken and put in a bottle containing some preservative The mo«t common preservatives now in use are bichromate of potash and corrosive sublimate, and only enough of either of these substances to keep the sample from thickening should be used.

The sample bottles should be kept plainly labelled or numbered, well covered, and in a dark place. In preparing the sample for te&ting the same care must be exercised as whea the sample was taken for the composite jar. No cream should be allowed to adhere to the iides of the bottle, noi any lumps show in the mixture. Before taking the sample the pipette should be rinsed with the milk that is to be tested. When delivering the milk to the bottle, place the end of the pipette against the side of the neck and then gradually release the pressure. Be sure to let the pipette deliver the milk slowly enough to permit the air to escape without taking any ot the milk with it. The last few drops should be blown out

of the pipette into the tent bottle, a"? it is important that all the milk should be delivered from the pipette to the bottle. The acid should be kept in a cool place. Never place it near your boiler or where the sun's rays will strike it. Sulphuric acid has a great affinity for water and should, therefore, be kept covered to exclude the moisture of the air, as this will shortly v. eakon its strength. It has b^en found that acid with a specific gravity ol 1.82 to 1.83 and a temperature of from 60dcg to 70deg Fahr for both acid and milk give? the best lesults. 17.5 C.C. of this, ecul is added to the test bottle, care being taken lo hold the bottle in a slanting position, so the acid may follow the glass rather than drop through the milk. Small \aiiations in the stiength of the acid may be counteracted by varying the quantity somewhat. In adding the acid all the milk should be washed down the neck of the bottle. To facilitate the mixture of the acid and milk the bottle hhould be given a rotary motion, but no milk should be allowed to get into the neck. As soon as the curdy matter is all difaolved the bottles should be placed in the centrifuge and whirled. By no means should the bottles be allowed to cool before whirling unless the temperature is» again raised before the opemtion takes place. After whirling five minutes the centrifuge is stopped and hot water is added until the bottles are filled to the ba*e of the necks. They are again whirled two minutes, when hot water is again added, filling the bottles to the 9 per cent. mark. After this they get a final whirling of one minute to bring all the separated fat into the neck of the bottle. It is very essential that the proper speed be maintained throughout eacb of these whirlings. In reading the fat column, the bottle must be held in an upright position, and the reading taken from the highest to the lowest fat limits. These readings should be taken in a room where the temperature is about 70deg Fahr., and be read as quickly and accurately as possible. If the room is much colder, or if many bo Hies are to be read, the bottles <-hould be placed in a hot-water bath until the readings are taken. The temperature of the fat at this stage should be about 130deg Fahr. The cleaning of the glassware is an important point in connection with the testing of milk, and unles3 this point has proper attention, accurate results cannot be obtained. The test bottles fchould be emptied as soon a» the tests are recorded. This prevents the fat from hardening on the neck oE the bottles, and the principal part is washed out with the hot liquid. The sample jars should never be emptied until after the readings have been taken and found satisfactory. As soon as emptied the bottles should he rinsed with warm water, and was-hed with some alkaline solution. After this they should be ringed with hot water, until they arc clean and bright.