In 1812, before the end of his apprenticeship, Faraday was engaged in experiments with voltaic batteries of his own construction. Having cut out seven discs of zinc the size of halfpence, and covered them with seven halfpence, he formed a pile by inserting pieces of paper soaked in common salt between each pair, and found that the pile so constructed was capable of decomposing Epsom salts. With a somewhat larger pile he decomposed copper sulphate and lead acetate, and made some experiments on the decomposition of water. On July 21, 1812, in writing to his friend Abbott, he mentions the movements of camphor when floating on water, and adds, "Science may be illustrated by those minute actions and effects, almost as much as by more evident and obvious phenomena.... My knife is so bad that I cannot mend my pen with it; it is now covered with copper, having been employed to precipitate that metal from the muriatic acid." Something of Faraday's disposition, as well as of the results of his self-education, may be gathered from the following quotations from letters to Abbott, written at this time:-- I have again gone over your letter, but am so blinded that I cannot see any subject except chlorine to write on; but before entering on what I intend shall fill up the letter, I will ask your pardon for having maintained an opinion against one who was so ready to give his own up. I suspect from that circumstance I am wrong.... In the present case I conceive that experiments may be divided into three classes: first, those which are for the old theory of oxymuriatic acid, and consequently oppose the new one; second, those which are for the new one, and oppose the old theory; and third, those which can be explained by both theories--apparently so only, for in reality a false theory can never explain a fact.