2IO 



THE PRESERVATION OF MILK. 



increasing its keeping properties. Boracic acid, both in the free 

 state and in the form of borax, is in great favour for this purpose, 

 and recourse is occasionally had to salicylic acid. F. M. HORN (I.) 

 records an instance where benzoic acid was used. All additions 

 of this kind are contrary to law and therefore punishable. 



128. Condensed Milk. 



It is not infrequently desirable to convert large quantities of 

 milk into a permanently stable condition for use as food, e.g. for 

 provisioning ships. In other cases, owing to local circumstances, 

 the milk production of a district may be far in excess of the local 



requirements, and con- 

 sequently the necessity 

 arises for converting the 

 product into a stable and 

 readily portable condition 

 for export. Many of the 

 Swiss Cantons, for ex- 

 ample, are in this posi- 

 tion. Such milk must 

 be capable of remaining 

 entirely unaltered for any 

 desired period (several 

 years), even when ex- 

 posed to tropical tem- 

 peratures, a condition 

 unattainable by any of 

 the means already de- 

 scribed. In former years 

 the opinion was current 



The black square represents the germ-content of raw that ^ s could be effected 

 milk per unit of space, that of the same sample by the method proposed 

 after Pasteurisation being shown by the small > \ j AI_ 



white square. (After Russell.) by Appert, and in the 



middle of the seventies, 



Nageli also attempted to attain this object by a similar (secret) 

 method of treatment. However, the "preserved milk" produced 

 by him (and not a few of his successors) failed to fulfil expecta- 

 tions, and equally unfavourable results attended the numerous 

 attempts made to render milk stable by so-called "Pasteurisa- 

 tion," i.e. by the prolonged action of a temperature of about 60 

 to 65 C., in connection with which subject N. L. RUSSELL (III.) 

 carried out a series of investigations (Fig. 51). All these methods, 

 as well as numerous others of allied nature such, for example, as 

 that devised by Soxhlet, and which Loeflund attempted to techni- 

 cally utilise have, however, been recognised as unreliable. At 

 present there is only one single way of arriving at the object in view, 

 and that is by thickening the milk and adding sugar. 



FIG. 5 i. 



Illustration of the effect of Pasteurising milk. 



