THE MILK CONTRACTOR 307 



trie cable. A high-tension current is used which in commercial practice necessi- 

 tates the use of devices to protect the operator. Prior to the entry into the lethal 

 tube the milk flows through an aluminum tube; similarly, as the milk leaves the 

 apparatus it flows through a second aluminum tube, both tubes having a direct 

 earth connection. This arrangement prevents any leakage of current into the 

 containing or receiving tanks. Thus attendants are protected against shock. 

 The lethal tube, with its high-voltage connections, is mounted on a slate panel, 

 itself suspended from the back of a glass-panelled upper cupboard. A lower 

 cupboard, the doors of which are automatically closed by the overlapping doors 

 of the upper cupboard, contains the high-voltage transformer. For further pro- 

 tection, in the framework of the two doors of the upper cupboard, switches are 

 placed, which, when the doors are open, are "off" t>ut when the doors are closed 

 are "on." These switches are connected directly with the source of the electric 

 current. When, therefore, the doors are open the electric current is of necessity 

 "off" and the apparatus can be worked only when the doors are closed; the act 

 of opening any of the doors automatically disconnects the electric current. Thus 

 the apparatus is perfectly safe even when worked by an operator not especially 

 skilled in the theory and practice of electricity. The electricity used, normally 

 consists of a low-voltage alternating current which is passed into a transformer 

 and the voltage increased to the desired point. Switches and other controlling 

 gear are mounted on a switchboard from which the whole apparatus is worked. 

 "The course of the milk through the apparatus is from a receiving tank into 

 a constant-level tank, into the lethal tube, into a covered channel which dis- 

 charges into each of two auxiliary tanks which empty into the main tank for 

 the heated milk. In starting the apparatus the milk on emerging from the 

 lethal tube is caught in a separate tank; the current is switched on and regulated, 

 when the correct speed of flow is established, the temperature of the milk rises 

 to the normal maximum and the sterilizing process begins. The milk that has 

 heretofore passed the lethal tube is returned to the receiving tank for steriliza- 

 tion. The object of the two auxiliary tanks is to make it possible to reject por- 

 tions of the batch that for one reason or another are thought to be imperfecly 

 sterilized before they reach the main tank." 



The apparatus effects satisfactory reduction in the number of bacteria 

 in the milk, and wholly destroys any B. coli and B. tuberculosis that are 

 present. It does not alter the chemical composition of the milk. 



The large-scale experimental plant was operated 3 months and in that 

 time heated some 9,000 gal. of milk which were distributed in 270,000 

 bottles for infant use. The total cost including interest and depreciation, 

 wages and fuel, when electricity is 1.5d. perunit is 1.25d. per gallon. In the 

 case of town's gas at 2s. 8d. per 1,000 cu. ft., the total cost is reduced to 96 

 d. per gallon and is again reduced to 85d. per gallon when producer gas, 

 obtained from anthracite at 30s. per ton, is used. The amount of elec- 

 tricity used is about 0.43 units per gallon of milk. 



Sterilization of Milk by Ultraviolet Rays. Preliminary experiments 

 on the sterilization of milk by ultraviolet rays were conducted by Ayres 

 and Johnson. They found that: 



