ALUMINIUM is acted on by acids with which it forms salts and also by solutions of certain salts, notably common salt, i.e. sodium chloride, with which it forms a double chloride.
There is always a certain amount of oxide on the surface of aluminium no matter how highly polished. This can easily be proved by rubbing a piece of aluminium with a clean white rag.
It may be argued that fruit acids are too weak a concentration to act on the metal, but, on the other hand, they are never too weak a concentration to form salts with the oxide. It is well known that boiling fruit in an aluminium saucepan will make the pan look bright and clean, and since the bulk of our fruits contain either citric, tartaric or malic acids, we should get either citrates, tartrates or malates of aluminium in our stewed or baked fruits.
Should a solution of an alkaline carbonate stand, even for a short time, in an aluminium vessel it will turn the inside of the vessel blackish, due to the formation of aluminium hydroxide or oxide. The soluble chlorides in our food, particularly the sodium chloride, would form double chlorides with this hydroxide or oxide, and the soluble sulphates would form double sulphates of alums. (Common alum is the double sulphates or aluminium or potassium and aluminium). Further, the sodium chloride attacks the metal itself without the intervention of an alkaline carbonate to form oxide.
In my apprenticeship days, I well remember salts and chlorides, it will be evident that aluminium utensils are not suitable for the cooking of vegetables and potatoes. In my opinion aluminium ware is suitable only for boiling water, heating milk (which should be done quickly) and for frying. It may be said that the amount of aluminium salts consumed per day through food cooked in aluminium ware must be very small, but multiplied by 365 it will be quite a respectable quantity at the end of the year. Aluminium salts precipitate albumen; their effects are therefore likely to be cumulative.
Some people are more susceptible to aluminium poisoning than others, and these susceptibles would naturally be the people to suffer most. Symptoms would at first be mild and indefinite, but would gradually increase and the cause would be very likely overlooked.