Croll claimed to be a chemical manufacturer in Greenwich. In 1836 a request to buy ammoniacal liquor from the Ratcliffe Company came from 'Croll and Jones'. 'Jones is intermittently listed between 1810 and 1838 in the Greenwich Rate Books. He made vitriol at the chemical works which had once been associated with the Greenwich copperas works. There is no sign of Croll in either ratebooks or directories. Perhaps his ammonia business was just a job in Jones' vitriol works.
Croll's chemical 'business' did badly. He then took a job as second engineer with the Chartered Gas Company at Brick Lane. It seems unlikely that the Chartered would have taken someone on in this senior post without experience of gas manufacture or supervision in a similar business. It rather leads to the suspicion that Croll's background was not quite what he later claimed. He was 'a young man .... full of ideas'. He was said to have been very effective, and happy, at Brick Lane. He had become a total abstainer and temperance beverages were provided in the works. Workmen were signed up to the cause. When he resigned after only five years work he was presented with a silver snuff box.
During the next ten years Croll took out eight patents, all but one concerned with the chemistry of coal gas and ammonia salts.
In this period it had become increasingly clear that gas purification methods ought to be improved in inner city gas works. The smell was insupportable and disposal methods difficult. There were numerous attempts to find a better, cleaner, way - most London gas works had tested several such. Some of those who formulated new methods of purification were chemists whose real aim was to recover ammonia.