CONTROL OF THE PUBLIC MILK SUPPLY 435 



dirty, watered and skimmed milk off the market. That they in some 

 measure do this is not to be doubted but the sediment of dirty milk can 

 be greatly reduced by careful straining and by centrifugalizing the 

 milk, and milk can be doctored by the use of condensed milk and by 

 other means to meet the lactometer test so that only in a limited way do 

 these tests detect dirt and fraud. The sediment test is usually performed 

 by passing a pint of milk through a Wisconsin or a Wizard sediment 

 tester. The sediment is caught on cotton disc which may be dried and 

 preserved. The test is one that every dairyman can grasp the meaning 

 of and it has been used very effectively not only by city officials but by 

 creameries and cheese factories to get cleaner milk. It is the practice 

 of some offices to mail excessively dirty discs to the offending producer 

 with an injunction that he mend his ways. Some health officers preserve 

 the discs and mount them on a card to be filed as part of the permanent 

 record of the dairyman ; others at intervals prepare a mount of the discs 

 of all the dairymen in town and display it in the health office or in some 

 store window where all who pass can see it. 



Lactometer Test. The lactometer is a float for taking the specific 

 gravity of milk. * There are two lactometers in use in this country, 

 the New York Board of Health and the Quevenne; they differ principally 

 in the scales on the stem for reading the specific gravity. The Quevenne 

 i$ probably in most general use; on its scale most normal milks give read- 

 ings between 30 and 34. 



Chemical Tests. The chemical determinations that are ordinarily 

 made in examining milk are the butterfat, the total solids and the ash. 

 The solids-not-fat are obtained by difference. The acidity of milk is 

 easily determined by titrating it with an alkali and with phenolphthalein 

 as an indicator. The acidity is usually expressed as percentage of lactic 

 acid. In the larger laboratories, if skimming is suspected, proteins are 

 determined by the Gunning method, if watering the refraction of the 

 serum, the lactose, the soluble albumen, and the sour serum ash. 



Tests for Preservatives. Tests for preservatives in milk are made at 

 most laboratories. Formerly this kind of adulteration was very common 

 but partly because of the vigor of the campaign against it and partly 

 because dairymen have learned to produce milk that will keep, the doping 

 of milk has gone out of fashion. The preservatives most commonly 

 used are formaldehyde, borax, borates, boracic acid, salicylic acid, ben- 

 zoic acid, benzoates, sodium bicarbonate, fluorids, hydrogen peroxid 

 (Buddeized milk), nitrates, potassium bichromate, etc. To cream, cal- 

 cium sucrate (viscogen) is sometimes added to thicken it; so is gelatin 

 and possibly starch. Anatto and the coal-tar dyes, principally the 

 azo-colors, are sometimes used to make milk look rich. 



Biological Tests. Determination of the Cellular Content. Biological 

 examination of milk is divided into two parts, namely : the determination 



