for (i=0; i<json.count; i++) {

    NSDictionary *bodyDictionary = [json objectAtIndex:i];
    NSDateFormatter *formatter = [[NSDateFormatter alloc]init];
    [formatter setTimeZone:[NSTimeZone timeZoneWithName:@"GMT"]];
    [formatter setLocale:[NSLocale currentLocale]];
    [formatter setDateFormat:@"yyyy-mm-dd HH:mm:ss"];
    NSDate *date = [formatter dateFromString:[bodyDictionary objectForKey:@"date"]];
    NSNumber* thisVolume = [NSNumber numberWithInteger:[[bodyDictionary objectForKey:@"volume"] integerValue]];

    NSTimeInterval timeNumber = [date timeIntervalSince1970];

    CGPoint point = CGPointMake(timeNumber, thisVolume.doubleValue);
    NSValue *pointValue = [NSValue valueWithCGPoint:point];
    [dataArray addObject:pointValue];

}