That Flockhart supplied Simpsons self-experiment on 4 November 1847, was not the original plan, but his method for ensuring the chemicals purity was still broadly being used in the 1960s. Another name for it, in his time, was a perchloride of formyle, which had been planned by Dr. Simpson to come from David Waldie, another Scottish doctor/chemist from Linlithgow, based in Liverpool , but the laboratory suffered a fire. The process of making it  could be dangerous; once one of their chloroform retorts exploded but Flockhart and Duncan both wore spectacles, which had protected their eyes.
The circumstances and different opinions on how Flockhart came to supply the surgeon with this drug is discussed in the Pharmaceutical Historian including statements by Simpsons daughter that Flockhart and his partner worked until 2 a.m. to prepare the first perchloride of formyle for her fathers trial. The success of the doctors experiment was communicated widely such that within three months demand was already high for this new anaesthetic and the firm were exporting to England.  Flockharts product was exhibited in the London 1851 Exhibition, and that year Simpson paid Flockhart to supply it to Florence Nightingale.  The total sales across the market was estimated as 750,000 doses a week by 1895.
From 1862 to 1875 the partners were Chemists and Druggists in Ordinary to Queen Victoria, supplying to Balmoral Castle, and she used chloroform in childbirth.
The firm extended to London and became the main supplier of chloroform in Britain, including to its armed forces,  which continued during both World Wars. Duncan, Flockhart and Company was also used for sourcing reference samples on chloroform quality by drug firms in the United States.
At the 1947 centenary of the chloroform use experiment, the companys contribution and Flockharts role was noted in the press.