idiom? "give someone a black at"

[imchongjun]

Hello, teachers!
I have a question about an idiomatic expression: "give someone a black".
I came across this expression while reading "The Great Impersonation" by Oppenheim, and checked several dictionaries and search engines on the web, but could not find its meaning nor similar expressions. What does it mean?

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"A game of pills, Eddy," he proposed. "They tell me that pool is one of your greatest accomplishments."

"I'm pretty useful," the young man confessed, with a satisfied chuckle. "Give you a black at snooker, what?"

Dominey took his arm and led him into the billiard-room.

"You will give me nothing, young fellow," he replied. "Set them up, and I will show you how I made a living for two months at Johannesberg!"
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[Mister Micawber]

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Eddy is offering Dominey a handicap of one black ball worth 7 points.

Set of Snooker balls: fifteen object balls that are not numbered and are solid red (called reds), six object balls of other colors that are not numbered (called colors) and a cue ball (called the white ball). Point values for object balls: red-1, yellow-2, green-3, brown-4, blue-5, pink-6, black-7.
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