Ons kook solank as die gassilinder nie leeg is nie.

Here solank as means as long as.

It introduces a condition that remains true for a period of time:

• Ons kook = we cook / we are cooking
• solank as die gassilinder nie leeg is nie = as long as the gas cylinder is not empty

So the idea is: the cooking continues while that condition holds.

A useful note: solank by itself can also mean for now or in the meantime in other sentences, but in this structure with a following clause, it means as long as.

Because standard Afrikaans usually uses a double negative frame.

In a simple main clause, you would say:

Die gassilinder is nie leeg nie.
= The gas cylinder is not empty.

The first nie introduces the negation, and the second nie closes it.

This is normal Afrikaans grammar, not an emphatic or unusual form. It does not mean a positive statement, the way a double negative sometimes can in English.

Because the part after solank as is a subordinate clause, and Afrikaans usually sends the finite verb to the end of a subordinate clause.

Compare:

• Main clause: Die gassilinder is nie leeg nie.
• Subordinate clause: ... as die gassilinder nie leeg is nie.

So:

• in the main clause, is comes early
• in the subordinate clause, is moves toward the end

The final nie still stays at the very end, so is appears just before it.

Afrikaans usually writes compound nouns as one word.

So:

• gas
  • silinder → gassilinder

This is very common in Afrikaans. English sometimes does this too, but less consistently.

The double s is just the normal spelling where the two parts meet. You do not write it as two separate words here.

die is the normal Afrikaans word for the.

A helpful difference from some other languages is that Afrikaans does not change the definite article for gender. So die can be used for:

• masculine nouns
• feminine nouns
• neuter nouns
• singular and plural

So die gassilinder simply means the gas cylinder.

It can mean either, depending on context.

Afrikaans often uses the simple present where English might use either:

• we cook
• we are cooking

So Ons kook can mean:

• a general action: we cook
• a current ongoing action: we are cooking

Context tells you which one is intended.

Yes, often you can.

A very natural version is:

Ons kook solank die gassilinder nie leeg is nie.

This still means We cook as long as the gas cylinder is not empty.

So both of these are possible:

• solank as
• solank

Learners will often see both. Solank as can feel a little more explicitly like English as long as, but solank alone is also common.

Yes. You can say:

Solank as die gassilinder nie leeg is nie, kook ons.

That means the same thing.

But notice the word order in the main clause:

• Ons kook ...
• Solank as ..., kook ons.

Afrikaans keeps the finite verb in the second position of the main clause, so when the subordinate clause comes first, kook comes before ons.

Because leeg is being used as a predicate adjective, after the verb is.

In:

Die gassilinder is leeg.
= The gas cylinder is empty.

the adjective stays in its basic form: leeg.

So in the negative subordinate clause:

... die gassilinder nie leeg is nie

it still remains leeg.

The positive version is:

Die gassilinder is leeg.
= The gas cylinder is empty.

Then the negative main-clause version is:

Die gassilinder is nie leeg nie.
= The gas cylinder is not empty.

And after solank as, that becomes:

... as die gassilinder nie leeg is nie.

Seeing these three side by side is a good way to understand how Afrikaans changes word order in subordinate clauses.