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.

Question: What was McGrigor's relationship to James Watt?
Self-contained rewrite: What was James McGrigor's relationship to James Watt?