CoMPOSITION AND PRopERTIES oF MILK 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 oyidation, 
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 which 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 invite 
chemical action of the acid and lactose of the milk on the copper 
surface of the container. Jf 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 powder 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 
Tt 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 1s reasonably permanent. 
