Analog pins as output by using digitalWrite

I am making a triac-controlled light dimmer. To control the triac I want to use pins A4 or A5, because others are occupied. I have tried the following functions and methods, but nothing seems to put the pins to HIGH state:

 1. pinMode(A4, OUTPUT);    
    digitalWrite(A4, HIGH);
 2. pinMode(18,OUTPUT);  
    digitalWrite(18,HIGH);
 3. DDRC |= (1 << DDC4);  
    PORTC |= (1 << PC4);

I have tried the same things with A5 and other A# pins to no avail. The only pin that works is A0. Only when the triac is connected to it, the lamp lights on.

Is this a valid way to set analog pins?

void setup(){  
  pinMode(A4, OUTPUT);  
}

void loop(){  
  digitalWrite(A4, HIGH);
}

• Edit: My code was quite messy, it appears that some other functions prevented from using pins A4 or A5. It is working now.
• It was the DS1307Emulator library. After initialization I had to use DS1307Emulator.busDisconnect(); Didn't know it uses I2C.