Amplifying what Yan has
discovered for us, the invaluable Wikipedia tells us that "Borax
was first discovered in dry lake beds in Tibet and was imported via
the Silk Road to Arabia.[6]
Borax first came into common use in the late 19th century . . . ."
So it would seem that Kipling had Purun Dass meet an early 'road
train'.
Alastair Wilson
