According to their meaning, we distinguish the following kinds of adverbial clauses:

An adverbial clause of time shows the time of the action expressed in the principal clause. Adverbial clauses of time are introduced by the following conjunctions: when, while, whenever, as, till, until, as soon as, as long as, since, after, before, now that.

My mother died when I was eight years old… (Eliot)
…we must strike while the iron’s hot. (Galsworthy)
I shall hope to visit you whenever I happen to be in London. (Collins)
There was still a gleam of sunset in the west as he strolled along. (Cronin)
Jan waved till the taxi disappeared round the bend in the road. (Cusack)
After this, they conversed on different subjects until they arrived at their journey’s end. (Dickens)
But as soon as I saw Susan I stopped noticing my surroundings. (Braine)
You can stay here as long as you want. (Hemingway)
She (June) had given him nothing of her company for a long time past, not in fact, since she had become engaged to Bosinney. (Galsworthy)
There was scarcely time for him to swallow a cup of tea in the refreshment room before the southbound train was signalled. (Cronin)
This is the claim I make on you, now that we have found each other. (Eliot)

#1. In some cases an adverbial clause of time introduced by the conjunction as has the meaning of the gradual development of a process.

As dark night drew on, the sea roughened. (Ch. Bronte)

Adverbial clauses in sentences of the following type are also clauses of time:

Scarcely had his hands touched her head, when she sighed deeply. (London)

Hardly had they entered the house, when a violent thunderstorm broke out. No sooner had I wiped one salt drop from my cheek, than another followed. (Ch. Bronte)

The peculiarity of such sentences is that the conjunctions when and than introducing adverbial clauses of time are correlated with the adverbs scarcely, hardly and no sooner in the principal clause.

#2. The conjunction when introducing adverbial clauses of time should not be confused with the adverb when introducing subject clauses, predicative clauses, object clauses, and attributive relative clauses. Compare the following examples:

And people love their homes, even when things are tough. (Gow and D’Usseau) (ADVERBIAL CLAUSE OF TIME)
The next thing to discover is when the paint was last seen without that smear.(Collins) (PREDICATIVE CLAUSE)
Nothing told her when the eyes of her friend were for an instant fixed upon her, when the mind of her friend for a moment wondered at the strange, new look in her face. (Hichens) (OBJECT CLAUSE)
There were moments when I felt all the misery of my friendlessness, all the peril of my dreadful responsibility. (Collins) (ATTRIBUTIVE RELATIVE CLAUSE)

#3. Adverbial clauses of time introduced by the subordinating conjunction while should not be confused with independent clauses introduced by the coordinating conjunction while.

There was a pause while he raised his cup and drank some tea. (Cronin)(ADVERBIAL CLAUSE OF TIME)
His face was disturbed and troubled, while his clothes were disarranged and untidy. (Conan Doyle) (INDEPENDENT CLAUSE)

An adverbial clause of place shows the place of the action expressed in the principal clause. Adverbial clauses of place are introduced by the conjunctions where and wherever.

…I am quite comfortable where I am. (Wilde)
I looked where she pointed. (Collins)
…the street singers and players were making their nightly pilgrimage, pausing, wherever they saw a lighted window or a dark figure on a balcony. (Hichens)

One should not confuse the conjunction where introducing adverbial clauses of place with the adverb where introducing subject clauses, predicative clauses, object clauses, and attributive relative clauses.

Deronda placed himself where he could see her… (Eliot) (ADVERBIAL CLAUSE OF PLACE)
This must be where my sister lives. This is where she came for a temporary lodging, soon after father’s death. (Dickens) (PREDICATIVE CLAUSE)
Artois wondered where they were going. (Hichens)(OBJECT CLAUSE)
He turned immediately towards the hearth where Silas Marner sat lulling the child. (Eliot) (ATTRIBUTIVE CLAUSE)

An adverbial clause of cause (reason) shows the cause of, the action expressed in the principal clause. Adverbial clauses of cause are introduced by the conjunctions as, because, since, for fear (that); in official style they may also be introduced by the conjunctions on the ground that, for the reason that and some others.

As he had a liking for the spot, he seldom let a week pass without paying it a visit. (Dickens)
Letters were infrequent in his world and not very welcome because more often than not they contained bad news. (Priestley)
Since he had a certain talent for composition, his English master encouraged him to write little pieces… for the college magazine. (Cronin)
He is suspicious and jealous for fear anyone else might want to share in his power. (Lawrence)

Adverbial clauses of purpose state the purpose of the action expressed in the principal clause. They are introduced by the conjunctions that, in order that, so that, lest and some others.

She kept her back to the window that he might not see her rising color.(Hardy)
Wounds sometimes must be opened in order that they may be healed.(Trollope)
I crouched against the wall of the gallery so that I should not be seen. (Du Maurier)
…he made all these exclamations in a carefully suppressed voice, lest the valet should overhear anything. (Dickens)

Adverbial clauses of condition state the condition which is necessary for the realization of the action expressed in the principal clause. They are introduced by the conjunctions if, unless, suppose, in case, on condition that, provided, etc.

If he is not here by the end of the week, I shall go after him. (Austen)
I do not wish you to be my wife unless you are bound to me by love. (Trollope)
… my father, just at the last, consented to let him teach you, on condition that he never attempted to see your mother. (Voyhich)
I will do anything you wish, my brother, provided it lies in my power.(Dickens)

Adverbial clauses of condition can be joined to the principal clause asyndetically. In this case we find inversion in the subordinate clause.

…should Frank marry to-morrow, I shall have no ground for blaming him.(Trollope)
Had she been an Englishwoman, Artois would have guessed her to be near fifty. (Hichens)

An adverbial clause of concession denotes the presence of some obstacle which nevertheless does not hinder the action expressed in the principal clause.

Adverbial clauses of concession are introduced by the following conjunctions and connectives: though, although, as [1], no matter how, however, whoever, whatever, whichever. In official style they may also be introduced by the conjunctions notwithstanding that, in spite-of the fact that.

I enjoyed that day, though we travelled slowly, though it was cold, though it rained. (Ch. Bronte)
Although the young man’s eyes remained upon him, he did not speak… (Cronin)
Troubled as he was, he never exposed his difficulties to her. (Dreiser)
However much we may differ on the question of metaphysics; I am convinced of your absolute integrity. (Cronin)
He went forward to meet his uncle prepared to suppress the agitation he must feel, whatever news he was to hear. (Eliot)

Adverbial clauses of result denote the result of the action expressed in the principal clause. Very often adverbial clauses of this type have an additional meaning of degree.

Adverbial clauses of pure result are introduced by the conjunction so that; they are usually separated from the principal clause by a comma.

Darkness had fallen and a keen blizzard was blowing, so that the streets were nearly deserted. (Conan Doyle)

Adverbial clauses of result with an additional meaning of degree are introduced by the conjunction that; in these cases we find the adverb so or the demonstrative pronoun such in the principal clause. Such clauses are not separated from the principal clause by a comma.

He is so weak physically that he can hardly move. (Shaw)
Tom was in ecstasies — in such ecstasies that he even controlled his tongue and was silent. (Twain)

Adverbial clauses of manner characterize in a general way the action expressed in the principal clause. They are usually introduced by the conjunction as. In adverbial clauses of manner the idea of comparison is often implied.

…she did exactly as he told her. (Hardy)
Joe left the house as he had entered it… (Cronin)

Adverbial clauses of comparison denote an action with which the action of the principal clause is compared. They are introduced by the conjunctions that, as, as… as, not so… as, as if, as though.

Mr. Direck’s broken Wrist healed sooner than he desired. (Wells)
We were going up the road as fast as we could. (Hemingway)
He was white and jaded, as if he had not slept for many nights. (Wells)
She could see his lips moving, from time to time, as though he were talking to himself. (Cronin)

Some grammarians number among complex sentences, containing an adverbial clause of comparison, sentences of the following type:

The more he reflected on the idea the more he liked it. (Galsworthy)
The nearer he drew to that grim citadel the faster his pulse raced. (Cronin)

This way of analysis is open to objection on the ground that in sentences of this type it is impossible to point out the principal and the subordinate clause as, strictly speaking, here we have mutual subordination.

Some of the conjunctions introducing adverbial clauses are polysemantic and can introduce different types of adverbial clauses. For instance, the conjunction as may introduce adverbial clauses of time, cause, manner, and comparison.

As he spoke there was a sharp ring at the bell. (Conan Doyle) (ADVERBIAL CLAUSE OF TIME)
As the morning was fine, and he had an hour on his hands, he crossed the river by the ferry, and strolled along a footpath through some meadows. (Dickens) (ADVERBIAL CLAUSE OF CAUSE)
The dog did as he was ordered. (Dickens) (ADVERBIAL CLAUSE OF MANNER)
She (Lillian) saw now that she did not love him (Cowperwood) as some women love their husbands. (Dreiser) (ADVERBIAL CLAUSE OF COMPARISON)

The conjunction since introduces adverbial clauses of time and cause.

It was a long time since I had written to the States…(Hemingway)(ADVERBIAL CLAUSE OF TIME)
Since the lunchroom was full, she sat at our table, and, reached out for the bill of fare. (King) (ADVERBIAL CLAUSE OF CAUSE)

The composite conjunction so that introduces adverbial clauses of result and purpose.

They were rich and I was poor, so that it was no easy matter for me to follow them. (Conan Doyle) (ADVERBIAL CLAUSE OF RESULT)
I turned away, so that Frith should not see my face. (Du Maurier)(ADVERBIAL CLAUSE OF PURPOSE)