80 PUBLIC HEALTH CHEMISTRY 



article has been rendered injurious to health, and that the 

 purchaser has been prejudiced in the above sense ; also 

 that similar presumption is raised where boron preserva- 

 tives are present in milk to an amount exceeding 57 parts 

 per 100,000 or 40 grains per gallon." A Departmental 

 Committee of the Board of Agriculture (1901) recom- 

 mended " that the use of any preservative or colouring 

 matter whatever in milk offered for sale in the United 

 Kingdom be constituted an offence under the Sale of Food 

 and Drugs Acts," but this recommendation has not yet 

 received the force of law. 



The commonest preservatives in use are boric acid or 

 borates and formic aldehyde (formaldehyde). Sodium 

 carbonate is sometimes added to restrain the formation of 

 lactic acid. Salicylic acid, benzoates, salt, sulphites, fluor- 

 ides, boro-glycerin, and hydrogen peroxide have all been 

 used at various times. 



1. Borax and Boric Acid. The ash of the milk is treated 

 with a little dilute HC1, so that it is distinctly but not 

 strongly acid, and a piece of turmeric paper is placed in 

 the liquid, and the dish is slightly warmed for a few minutes. 

 The turmeric paper is removed and dried at a low tempera- 

 ture. If even so small a quantity as o-oi per cent (1 in 

 10,000) of boric acid be present it will produce on the paper 

 a reddish colour when dry. On moistening with a drop 

 of an alkaline solution the red turns a greenish black. 

 Boric acid and borates are the only substances which will 

 give this change of colour in an acid solution. 



Richmond's Test. Take equal quantities of the milk 

 sample in two test tubes, and add N/10 caustic soda to 

 each, drop by drop, until a faint pink colour appears. To 

 one tube add an equal quantity of water, and to the other 

 the same quantity of neutral 50 per cent solution of gly- 

 cerin. If boric acid be present, the latter tube will turn 

 white, while in its absence both will remain the same colour. 



Another test is to take part of ash and add strong sul- 

 phuric acid and some alcohol. Put in a dark place and 

 light the alcohol, when in the presence of boric acid it 

 burns with a green flame. 



2. Formaldehyde. (1) Hehner's test. Take 5 c.c. of milk 

 in a test tube and add as much water. Some 90 per cent 



