Conversation so far:
What was the first chemical experiment?
From an early age Watt was very interested in chemistry.
When did he start doing chemical experiments?
in March 1788, McGrigor was able to bleach 1500 yards of cloth to his satisfaction.
What was McGrigor's relationship to James Watt?
By 1794 Watt had been chosen by Thomas Beddoes to manufacture apparatus to produce.
What was the name of their company?
CANNOTANSWER.
How long did he work with McGrigor?
Watt continued to experiment with various gases for several years, but by 1797 the medical uses for the "factitious airs" had come to a dead end.
What did he do after that?
CANNOTANSWER.

Question: What was his most important chemical experiment?
Self-contained rewrite: What was James Watt's most important chemical experiment?