COMPOSITION AND PROPERTIES OF Miuc POWDERS 327 



and salts are most active oxidizers. This is especially the case of 

 copper and its alloys, such as brass and German silver ; also the salts 

 of copper. Iron, while not inert from the standpoint of oridation, 

 is much less active and its salts exert but a slight oxidizing action. 

 Tin and nickel have no oxidizing action. 



On the basis of these facts it is not improbable, that the 

 holding, heating- and condensing of milk in copper containers, 

 and the use of copper drums in film-drying and of brass nozzles 

 in spray-drying, are factors contributory to the deterioration of 

 the resulting milk powders. 



Continuous, or flash heaters through w<hich the milk passes 

 rapidly and to the metal surfaces of which it is exposed for a 

 very short time only, are a negligible factor in this respect. 

 Even if these surfaces are of untinned copper, there is but very 

 remote danger of damage to the product. 



But not so with containers in which the milk is held for 

 hours, or in which it is condensed prior to desiccation. Here 

 the time and conditions of exposure are sufficient to 1 invite 

 chemical action of the acid and lactose of the milk on the copper 

 surface of the container. If the holding tanks are of copper, 

 they should be heavily tinned ; or in their place glass enameled 

 tanks should be used. 



The copper vacuum pan is another menace to keeping- 

 quality. Salts of copper are especially likely to form on the 

 inner surface of the dome which is exposed to the spray and to 

 the volatile acids of the boiling milk. After each day's work 

 the dome, as well as all the other parts of the interior of the 

 pan, should be scrupulously cleaned to prevent any accumulation 

 of copper salts, which would otherwise become a part of the 

 next batch and of the milk pow r der made therefrom. 



In the manufacture of whole milk powder, particularly, due 

 to the action of the copper of the vacuum pan on the butterfat, 

 the tendency to cause damage to the finished product; is great. 

 It is advisable to skim the whole milk, condense the skim milk 

 only and add the cream after condensing, in order to minimize 

 this danger. 



Sandblasted iron pipes are preferable to so called sanitary 

 pipes, unless the inside copper surface of the sanitary pipes is 

 properly tinned and the tin coating is reasonably permanent. 



