Conversation so far:
What was James Watt's first chemical experiment?
James Watt had already found that an aqueous solution of chlorine could bleach textiles, and had published his findings.
When did James Watt start doing chemical experiments?
In late 1786, James Watt discovered that mixing salt, manganese dioxide, and sulphuric acid could produce chlorine. This would improve the cloth bleaching process.
What was James McGrigor's relationship to James Watt?
James McGrigor was James Watt's father-in-law.
What was the name of the company that James Watt founded with Matthew Boulton in 1775?
The new firm of Boulton and Watt was eventually highly successful and James Watt became a wealthy man.

Question: How long did he work with McGrigor?
Self-contained rewrite: How long did James Watt work with James McGrigor?